diff --git a/Cargo.lock b/Cargo.lock
index 5dcadf7e0..7d277b45f 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -35,6 +35,7 @@ dependencies = [
  "hostname 0.0.1",
  "id 0.0.1",
  "install 0.0.1",
+ "join 0.0.1",
  "kill 0.0.1",
  "lazy_static 0.2.10 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.33 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -588,6 +589,14 @@ dependencies = [
  "either 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "join"
+version = "0.0.1"
+dependencies = [
+ "getopts 0.2.15 (registry+https://github.com/rust-lang/crates.io-index)",
+ "uucore 0.0.1",
+]
+
 [[package]]
 name = "kernel32-sys"
 version = "0.2.2"
diff --git a/Cargo.toml b/Cargo.toml
index 3148e261c..fdc46a845 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -69,6 +69,7 @@ fuchsia = [
 generic = [
   "cat",
   "hashsum",
+  "join",
   "more",
   "ln",
   "ls",
@@ -178,6 +179,7 @@ hostid   = { optional=true, path="src/hostid" }
 hostname = { optional=true, path="src/hostname" }
 id       = { optional=true, path="src/id" }
 install  = { optional=true, path="src/install" }
+join     = { optional=true, path="src/join" }
 kill     = { optional=true, path="src/kill" }
 link     = { optional=true, path="src/link" }
 ln       = { optional=true, path="src/ln" }
diff --git a/Makefile b/Makefile
index 4bc976e13..84510df71 100644
--- a/Makefile
+++ b/Makefile
@@ -61,6 +61,7 @@ PROGS       := \
   fold \
   hashsum \
   head \
+  join \
   link \
   ln \
   ls \
diff --git a/src/join/Cargo.toml b/src/join/Cargo.toml
new file mode 100644
index 000000000..9c7fc6bfa
--- /dev/null
+++ b/src/join/Cargo.toml
@@ -0,0 +1,16 @@
+[package]
+name = "join"
+version = "0.0.1"
+authors = []
+
+[lib]
+name = "uu_join"
+path = "join.rs"
+
+[dependencies]
+getopts = "0.2.14"
+uucore = { path="../uucore" }
+
+[[bin]]
+name = "join"
+path = "main.rs"
diff --git a/src/join/join.rs b/src/join/join.rs
new file mode 100644
index 000000000..5f257268a
--- /dev/null
+++ b/src/join/join.rs
@@ -0,0 +1,374 @@
+#![crate_name = "uu_join"]
+
+/*
+ * This file is part of the uutils coreutils package.
+ *
+ * (c) Konstantin Pospelov <kupospelov@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+extern crate getopts;
+
+#[macro_use]
+extern crate uucore;
+
+use std::fs::File;
+use std::io::{BufRead, BufReader, Lines, Read, stdin};
+use std::cmp::Ordering;
+
+static NAME: &'static str = "join";
+static VERSION: &'static str = env!("CARGO_PKG_VERSION");
+
+#[derive(PartialEq)]
+enum FileNum {
+    None,
+    File1,
+    File2,
+}
+
+struct Settings {
+    key1: usize,
+    key2: usize,
+    print_unpaired: FileNum,
+    ignore_case: bool,
+}
+
+impl Default for Settings {
+    fn default() -> Settings {
+        Settings {
+            key1: 0,
+            key2: 0,
+            print_unpaired: FileNum::None,
+            ignore_case: false,
+        }
+    }
+}
+
+struct Line {
+    fields: Vec<String>,
+}
+
+impl Line {
+    fn new(string: String) -> Line {
+        Line { fields: string.split_whitespace().map(|s| String::from(s)).collect() }
+    }
+
+    /// Get field at index.
+    fn get_field(&self, index: usize) -> &str {
+        if index < self.fields.len() {
+            &self.fields[index]
+        } else {
+            ""
+        }
+    }
+
+    /// Iterate each field except the one at the index.
+    fn foreach_except<F>(&self, index: usize, f: &F)
+    where
+        F: Fn(&String),
+    {
+        for (i, field) in self.fields.iter().enumerate() {
+            if i != index {
+                f(&field);
+            }
+        }
+    }
+}
+
+struct State {
+    key: usize,
+    print_unpaired: bool,
+    lines: Lines<BufReader<Box<Read>>>,
+    seq: Vec<Line>,
+}
+
+impl State {
+    fn new(name: &str, key: usize, print_unpaired: bool) -> State {
+        let f: Box<Read> = if name == "-" {
+            Box::new(stdin()) as Box<Read>
+        } else {
+            match File::open(name) {
+                Ok(file) => Box::new(file) as Box<Read>,
+                Err(err) => crash!(1, "{}: {}", name, err),
+            }
+        };
+
+        State {
+            key: key,
+            print_unpaired: print_unpaired,
+            lines: BufReader::new(f).lines(),
+            seq: Vec::new(),
+        }
+    }
+
+    /// Compare the key fields of the two current lines.
+    fn compare(&self, other: &State, ignore_case: bool) -> Ordering {
+        let key1 = self.seq[0].get_field(self.key);
+        let key2 = other.seq[0].get_field(other.key);
+
+        compare(key1, key2, ignore_case)
+    }
+
+    /// Skip the current unpaired line.
+    fn skip_line(&mut self) {
+        if self.print_unpaired {
+            self.print_unpaired_line(&self.seq[0]);
+        }
+
+        self.next_line();
+    }
+
+    /// Move to the next line, if any.
+    fn next_line(&mut self) {
+        match self.read_line() {
+            Some(line) => {
+                self.seq[0] = line;
+            }
+            None => {
+                self.seq.clear();
+            }
+        }
+    }
+
+    /// Keep reading line sequence until the key does not change, return
+    /// the first line whose key differs.
+    fn extend(&mut self, ignore_case: bool) -> Option<Line> {
+        while let Some(line) = self.read_line() {
+            let diff = compare(
+                self.seq[0].get_field(self.key),
+                line.get_field(self.key),
+                ignore_case,
+            );
+
+            if diff == Ordering::Equal {
+                self.seq.push(line);
+            } else {
+                return Some(line);
+            }
+        }
+
+        return None;
+    }
+
+    /// Combine two line sequences.
+    fn combine(&self, other: &State) {
+        let key = self.seq[0].get_field(self.key);
+
+        for line1 in &self.seq {
+            for line2 in &other.seq {
+                print!("{}", key);
+                line1.foreach_except(self.key, &print_field);
+                line2.foreach_except(other.key, &print_field);
+                println!();
+            }
+        }
+    }
+
+    /// Reset with the next line.
+    fn reset(&mut self, next_line: Option<Line>) {
+        self.seq.clear();
+
+        if let Some(line) = next_line {
+            self.seq.push(line);
+        }
+    }
+
+    fn has_line(&self) -> bool {
+        !self.seq.is_empty()
+    }
+
+    fn initialize(&mut self) {
+        if let Some(line) = self.read_line() {
+            self.seq.push(line);
+        }
+    }
+
+    fn finalize(&mut self) {
+        if self.has_line() && self.print_unpaired {
+            self.print_unpaired_line(&self.seq[0]);
+
+            while let Some(line) = self.read_line() {
+                self.print_unpaired_line(&line);
+            }
+        }
+    }
+
+    fn read_line(&mut self) -> Option<Line> {
+        match self.lines.next() {
+            Some(value) => Some(Line::new(value.expect("error reading file"))),
+            None => None,
+        }
+    }
+
+    fn print_unpaired_line(&self, line: &Line) {
+        print!("{}", line.get_field(self.key));
+        line.foreach_except(self.key, &print_field);
+        println!();
+    }
+}
+
+pub fn uumain(args: Vec<String>) -> i32 {
+    let mut settings: Settings = Default::default();
+    let mut opts = getopts::Options::new();
+
+    opts.optflag("h", "help", "display this help and exit");
+    opts.optopt(
+        "a",
+        "",
+        "also print unpairable lines from file FILENUM, where FILENUM is 1 or 2, corresponding to FILE1 or FILE2",
+        "FILENUM"
+    );
+    opts.optflag(
+        "i",
+        "ignore-case",
+        "ignore differences in case when comparing fields",
+    );
+    opts.optopt("j", "", "equivalent to '-1 FIELD -2 FIELD'", "FIELD");
+    opts.optopt("1", "", "join on this FIELD of file 1", "FIELD");
+    opts.optopt("2", "", "join on this FIELD of file 2", "FIELD");
+
+    let matches = match opts.parse(&args[1..]) {
+        Ok(m) => m,
+        Err(f) => crash!(1, "Invalid options\n{}", f),
+    };
+
+    if matches.opt_present("help") {
+        let msg = format!(
+            "{0} {1}
+Usage:
+ {0} [OPTION]... FILE1 FILE2
+
+For each pair of input lines with identical join fields, write a line to
+standard output. The default join field is the first, delimited by blanks.",
+            NAME,
+            VERSION
+        );
+        print!("{}", opts.usage(&msg));
+        return 0;
+    }
+
+    let keys = parse_field_number(matches.opt_str("j"));
+    let key1 = parse_field_number(matches.opt_str("1"));
+    let key2 = parse_field_number(matches.opt_str("2"));
+
+    settings.print_unpaired = match matches.opt_str("a") {
+        Some(value) => {
+            match &value[..] {
+                "1" => FileNum::File1,
+                "2" => FileNum::File2,
+                value => crash!(1, "invalid file number: {}", value),
+            }
+        }
+        None => FileNum::None,
+    };
+    settings.ignore_case = matches.opt_present("ignore-case");
+    settings.key1 = get_field_number(keys, key1);
+    settings.key2 = get_field_number(keys, key2);
+
+    let files = matches.free;
+    let file_count = files.len();
+
+    if file_count < 1 {
+        crash!(1, "missing operand");
+    } else if file_count < 2 {
+        crash!(1, "missing operand after '{}'", files[0]);
+    } else if file_count > 2 {
+        crash!(1, "extra operand '{}'", files[2]);
+    }
+
+    if files[0] == "-" && files[1] == "-" {
+        crash!(1, "both files cannot be standard input");
+    }
+
+    exec(files, &settings)
+}
+
+fn exec(files: Vec<String>, settings: &Settings) -> i32 {
+    let mut state1 = State::new(
+        &files[0],
+        settings.key1,
+        settings.print_unpaired == FileNum::File1,
+    );
+
+    let mut state2 = State::new(
+        &files[1],
+        settings.key2,
+        settings.print_unpaired == FileNum::File2,
+    );
+
+    state1.initialize();
+    state2.initialize();
+
+    while state1.has_line() && state2.has_line() {
+        let diff = state1.compare(&state2, settings.ignore_case);
+
+        match diff {
+            Ordering::Less => {
+                state1.skip_line();
+            }
+            Ordering::Greater => {
+                state2.skip_line();
+            }
+            Ordering::Equal => {
+                let next_line1 = state1.extend(settings.ignore_case);
+                let next_line2 = state2.extend(settings.ignore_case);
+
+                state1.combine(&state2);
+
+                state1.reset(next_line1);
+                state2.reset(next_line2);
+            }
+        }
+    }
+
+    state1.finalize();
+    state2.finalize();
+
+    0
+}
+
+/// Check that keys for both files and for a particular file are not
+/// contradictory and return the zero-based key index.
+fn get_field_number(keys: Option<usize>, key: Option<usize>) -> usize {
+    if let Some(keys) = keys {
+        if let Some(key) = key {
+            if keys != key {
+                crash!(1, "incompatible join fields {}, {}", keys, key);
+            }
+        }
+
+        return keys - 1;
+    }
+
+    match key {
+        Some(key) => key - 1,
+        None => 0,
+    }
+}
+
+/// Parse the specified field string as a natural number and return it.
+fn parse_field_number(value: Option<String>) -> Option<usize> {
+    match value {
+        Some(value) => {
+            match value.parse() {
+                Ok(result) if result > 0 => Some(result),
+                _ => crash!(1, "invalid field number: '{}'", value),
+            }
+        }
+        None => None,
+    }
+}
+
+fn compare(field1: &str, field2: &str, ignore_case: bool) -> Ordering {
+    if ignore_case {
+        field1.to_lowercase().cmp(&field2.to_lowercase())
+    } else {
+        field1.cmp(field2)
+    }
+}
+
+fn print_field(field: &String) {
+    print!("{}{}", ' ', field);
+}
diff --git a/src/join/main.rs b/src/join/main.rs
new file mode 100644
index 000000000..ee56bc720
--- /dev/null
+++ b/src/join/main.rs
@@ -0,0 +1,5 @@
+extern crate uu_join;
+
+fn main() {
+    std::process::exit(uu_join::uumain(std::env::args().collect()));
+}
diff --git a/tests/fixtures/join/capitalized.txt b/tests/fixtures/join/capitalized.txt
new file mode 100644
index 000000000..322f0d316
--- /dev/null
+++ b/tests/fixtures/join/capitalized.txt
@@ -0,0 +1,4 @@
+A 1
+B 2
+C 4
+D 8
diff --git a/tests/fixtures/join/case_insensitive.expected b/tests/fixtures/join/case_insensitive.expected
new file mode 100644
index 000000000..da91427a5
--- /dev/null
+++ b/tests/fixtures/join/case_insensitive.expected
@@ -0,0 +1,3 @@
+A 1 2 f
+B 2 3 g
+C 4 4 h
diff --git a/tests/fixtures/join/default.expected b/tests/fixtures/join/default.expected
new file mode 100644
index 000000000..5b3643826
--- /dev/null
+++ b/tests/fixtures/join/default.expected
@@ -0,0 +1,5 @@
+1 a
+2 b
+3 c
+5 e
+8 h
diff --git a/tests/fixtures/join/different_field.expected b/tests/fixtures/join/different_field.expected
new file mode 100644
index 000000000..fa9181ada
--- /dev/null
+++ b/tests/fixtures/join/different_field.expected
@@ -0,0 +1,6 @@
+2 b a f
+3 c b g
+4 d c h
+5 e f i
+6 f g j
+7 g h k
diff --git a/tests/fixtures/join/different_fields.expected b/tests/fixtures/join/different_fields.expected
new file mode 100644
index 000000000..cd870783f
--- /dev/null
+++ b/tests/fixtures/join/different_fields.expected
@@ -0,0 +1,5 @@
+c 3 2 1 cd
+d 4 3 2 de
+e 5 5 3 ef
+f 6 7 4 fg
+g 7 11 5 gh
diff --git a/tests/fixtures/join/empty.txt b/tests/fixtures/join/empty.txt
new file mode 100644
index 000000000..e69de29bb
diff --git a/tests/fixtures/join/fields_1.txt b/tests/fixtures/join/fields_1.txt
new file mode 100644
index 000000000..24d5fc285
--- /dev/null
+++ b/tests/fixtures/join/fields_1.txt
@@ -0,0 +1,5 @@
+1
+2
+3
+5
+8
diff --git a/tests/fixtures/join/fields_2.txt b/tests/fixtures/join/fields_2.txt
new file mode 100644
index 000000000..5b0d49021
--- /dev/null
+++ b/tests/fixtures/join/fields_2.txt
@@ -0,0 +1,9 @@
+1 a
+2 b
+3 c
+4 d
+5 e
+6 f
+7 g
+8 h
+9 i
diff --git a/tests/fixtures/join/fields_3.txt b/tests/fixtures/join/fields_3.txt
new file mode 100644
index 000000000..4c5c0e779
--- /dev/null
+++ b/tests/fixtures/join/fields_3.txt
@@ -0,0 +1,6 @@
+a 2 f
+b 3 g
+c 4 h
+f 5 i
+g 6 j
+h 7 k
diff --git a/tests/fixtures/join/fields_4.txt b/tests/fixtures/join/fields_4.txt
new file mode 100644
index 000000000..680e07c8d
--- /dev/null
+++ b/tests/fixtures/join/fields_4.txt
@@ -0,0 +1,5 @@
+2 c 1 cd
+3 d 2 de
+5 e 3 ef
+7 f 4 fg
+11 g 5 gh
diff --git a/tests/fixtures/join/unpaired_lines.expected b/tests/fixtures/join/unpaired_lines.expected
new file mode 100644
index 000000000..1cf8624b9
--- /dev/null
+++ b/tests/fixtures/join/unpaired_lines.expected
@@ -0,0 +1,9 @@
+1 a
+2 a f b
+3 b g c
+4 c h d
+5 f i e
+6 g j f
+7 h k g
+8 h
+9 i
diff --git a/tests/test_join.rs b/tests/test_join.rs
new file mode 100644
index 000000000..71f896fa4
--- /dev/null
+++ b/tests/test_join.rs
@@ -0,0 +1,95 @@
+use common::util::*;
+
+
+#[test]
+fn empty_files() {
+    new_ucmd!()
+        .arg("empty.txt")
+        .arg("empty.txt")
+        .succeeds().stdout_only("");
+
+    new_ucmd!()
+        .arg("empty.txt")
+        .arg("fields_1.txt")
+        .succeeds().stdout_only("");
+
+    new_ucmd!()
+        .arg("fields_1.txt")
+        .arg("empty.txt")
+        .succeeds().stdout_only("");
+}
+
+#[test]
+fn empty_intersection() {
+    new_ucmd!()
+        .arg("fields_1.txt")
+        .arg("fields_2.txt")
+        .arg("-2")
+        .arg("2")
+        .succeeds().stdout_only("");
+}
+
+#[test]
+fn default_arguments() {
+    new_ucmd!()
+        .arg("fields_1.txt")
+        .arg("fields_2.txt")
+        .succeeds().stdout_only_fixture("default.expected");
+}
+
+#[test]
+fn different_fields() {
+    new_ucmd!()
+        .arg("fields_2.txt")
+        .arg("fields_4.txt")
+        .arg("-j")
+        .arg("2")
+        .succeeds().stdout_only_fixture("different_fields.expected");
+
+    new_ucmd!()
+        .arg("fields_2.txt")
+        .arg("fields_4.txt")
+        .arg("-1")
+        .arg("2")
+        .arg("-2")
+        .arg("2")
+        .succeeds().stdout_only_fixture("different_fields.expected");
+}
+
+#[test]
+fn different_field() {
+    new_ucmd!()
+        .arg("fields_2.txt")
+        .arg("fields_3.txt")
+        .arg("-2")
+        .arg("2")
+        .succeeds().stdout_only_fixture("different_field.expected");
+}
+
+#[test]
+fn unpaired_lines() {
+    new_ucmd!()
+        .arg("fields_2.txt")
+        .arg("fields_3.txt")
+        .arg("-a")
+        .arg("1")
+        .succeeds().stdout_only_fixture("fields_2.txt");
+
+    new_ucmd!()
+        .arg("fields_3.txt")
+        .arg("fields_2.txt")
+        .arg("-1")
+        .arg("2")
+        .arg("-a")
+        .arg("2")
+        .succeeds().stdout_only_fixture("unpaired_lines.expected");
+}
+
+#[test]
+fn case_insensitive() {
+    new_ucmd!()
+        .arg("capitalized.txt")
+        .arg("fields_3.txt")
+        .arg("-i")
+        .succeeds().stdout_only_fixture("case_insensitive.expected");
+}
diff --git a/tests/tests.rs b/tests/tests.rs
index f8d20ec0e..d7d1032fa 100644
--- a/tests/tests.rs
+++ b/tests/tests.rs
@@ -58,6 +58,7 @@ generic! {
     "fold", test_fold;
     "hashsum", test_hashsum;
     "head", test_head;
+    "join", test_join;
     "link", test_link;
     "ln", test_ln;
     "ls", test_ls;