diff --git a/README.md b/README.md
index d5cbc27..c8cbda1 100644
--- a/README.md
+++ b/README.md
@@ -23,3 +23,33 @@ into the Rust code.
 
 Documentation of specific syntax features of husht will be added as they are
 implemented.
+
+## Usage
+
+`husht [options] [sources]`
+
+Transforms some files from husht to Rust. The source specification `sources`
+is a list of files, directories or glob patterns, defaulting to `.`. A
+directory `dir` is interpreted the same way as the glob pattern `dir/**` --
+in other words, all files recursively within that directory. Glob patterns
+are matched and all matching files are added to the list of files to process.
+All files in the output directory are ignored. Files that do not have
+extension `.toml` or `.hsh` are ignored. The former are copied unchanged;
+the latter are transformed per the husht language specification into
+Rust `.rs` files.
+
+Options:
+  - -h, --help -- Print a usage summary and exit
+  - --out-dir [dir] -- Specifies the output directory of the transformed
+    file(s), defaulting to `rust`. The transform of each source file is
+    written into the output directory, preserving its relative path to its
+    "root". The root of a file added by virtue of a glob is the top level
+    directory of that glob pattern, or the current directory if none.
+    The root of a file specified explicitly is the current directory.
+
+For example, if the `src` directory contains `main.hsh`, `sub/crate.hsh`, and
+`Cargo.toml` (and there are no other .hsh or .toml files in the directory
+tree), then `husht src` would write `rust/main.rs`, `rust/sub/crate.rs`, and
+`rust/Cargo.toml`. On the other hand just `husht`, defaulting to `husht .`,
+would write `rust/src/main.rs`, `rust/src/sub/crate.rs`, and
+`rust/src/Cargo.toml`.