diff --git a/README.md b/README.md
index 3962242..f96c612 100644
--- a/README.md
+++ b/README.md
@@ -29,9 +29,10 @@ test passes. In this way, each line is an assertion of truth.
 
 To run your tests, invoke the `bats` interpreter with a path to a test
 file. The file's test cases are run sequentially and in isolation, and
-the results are written to standard output in human-readable TAP
-format. If all the test cases pass, `bats` exits with a `0` status
-code. If there is a failure, `bats` exits with a `1` status code.
+the results are written to standard output in human-readable [TAP
+format](http://testanything.org/wiki/index.php/TAP_specification#THE_TAP_FORMAT).
+If all the test cases pass, `bats` exits with a `0` status code. If
+there are any failures, `bats` exits with a `1` status code.
 
     $ bats addition.bats
     1..2
@@ -46,3 +47,40 @@ fixtures, set up your environment, and clean up when you're done.
 
 Bats is most useful when testing software written in Bash, but you can
 use it to test any UNIX program.
+
+### The `run` helper
+
+You're probably most interested in testing a command's exit status and
+output. Bats includes a `run` helper that invokes its arguments as a
+command, saves the exit status and output into special global
+variables, and then returns with a `0` exit status so you can continue
+to make assertions in your test case.
+
+For example, let's say you're testing that the `foo` command, when
+passed a nonexistent filename, exits with a `1` status code and prints
+an error message.
+
+```bash
+@test "invoking foo with a nonexistent file prints an error" {
+  run foo nonexistent_filename
+  [ "$status" -eq 1 ]
+  [ "$output" = "foo: no such file 'nonexistent_filename'" ]
+}
+```
+
+The `$status` variable contains the status code of the command, and
+the `$output` variable contains the combined contents of the command's
+standard output and standard error streams.
+
+A third special variable, the `$lines` array, is available for easily
+accessing individual lines of output. For example, if you want to test
+that invoking `foo` without any arguments prints usage information on
+the first line:
+
+```bash
+@test "invoking foo without arguments prints usage" {
+  run foo
+  [ "$status" -eq 1 ]
+  [ "${lines[0]}" = "usage: foo <filename>" ]
+}
+```