diff --git a/README.md b/README.md
index 67f8dda..e18f6ee 100644
--- a/README.md
+++ b/README.md
@@ -43,12 +43,13 @@ necessary for fetching and updating the packages.
 * [Update](#update): updates one or all packages in `nix/sources.json`.
 * [Drop](#drop): deletes a package from `nix/sources.json`.
 
-`niv` has two more utility functions:
+`niv` has some utility functions:
 
 * [Init](#init): bootstraps a Nix project, in particular creates a
   `nix/sources.json` file containing `niv` and `nixpkgs` as well as a
   `nix/sources.nix` file that returns the sources as a Nix object.
 * [Show](#show): shows the packages' information.
+* [Modify](#modify): modifies attributes _without_ performing an update.
 
 ### Configuration
 
@@ -217,7 +218,8 @@ Available commands:
   add                      Add a GitHub dependency
   show                     
   update                   Update dependencies
-  modify                   Modify dependency
+  modify                   Modify dependency attributes without performing an
+                           update
   drop                     Drop dependency
 
 ```
@@ -293,6 +295,38 @@ Available options:
 
 ```
 
+#### Modify
+
+```
+Examples:
+
+  niv modify nixpkgs -v beta-0.2
+  niv modify nixpkgs -a branch=nixpkgs-unstable
+
+Usage: niv modify PACKAGE ([-a|--attribute KEY=VAL] |
+                  [-s|--string-attribute KEY=VAL] | [-b|--branch BRANCH] |
+                  [-o|--owner OWNER] | [-r|--repo REPO] | [-v|--version VERSION]
+                  | [-t|--template URL] | [-T|--type TYPE])
+  Modify dependency attributes without performing an update
+
+Available options:
+  -a,--attribute KEY=VAL   Set the package spec attribute <KEY> to <VAL>, where
+                           <VAL> may be JSON.
+  -s,--string-attribute KEY=VAL
+                           Set the package spec attribute <KEY> to <VAL>.
+  -b,--branch BRANCH       Equivalent to --attribute branch=<BRANCH>
+  -o,--owner OWNER         Equivalent to --attribute owner=<OWNER>
+  -r,--repo REPO           Equivalent to --attribute repo=<REPO>
+  -v,--version VERSION     Equivalent to --attribute version=<VERSION>
+  -t,--template URL        Used during 'update' when building URL. Occurrences
+                           of <foo> are replaced with attribute 'foo'.
+  -T,--type TYPE           The type of the URL target. The value can be either
+                           'file' or 'tarball'. If not set, the value is
+                           inferred from the suffix of the URL.
+  -h,--help                Show this help text
+
+```
+
 #### Drop
 
 ```
diff --git a/README.tpl.md b/README.tpl.md
index b99d3da..08643df 100644
--- a/README.tpl.md
+++ b/README.tpl.md
@@ -43,12 +43,13 @@ necessary for fetching and updating the packages.
 * [Update](#update): updates one or all packages in `nix/sources.json`.
 * [Drop](#drop): deletes a package from `nix/sources.json`.
 
-`niv` has two more utility functions:
+`niv` has some utility functions:
 
 * [Init](#init): bootstraps a Nix project, in particular creates a
   `nix/sources.json` file containing `niv` and `nixpkgs` as well as a
   `nix/sources.nix` file that returns the sources as a Nix object.
 * [Show](#show): shows the packages' information.
+* [Modify](#modify): modifies attributes _without_ performing an update.
 
 ### Configuration
 
@@ -216,6 +217,12 @@ replace_niv_add_help
 replace_niv_update_help
 ```
 
+#### Modify
+
+```
+replace_niv_modify_help
+```
+
 #### Drop
 
 ```
diff --git a/default.nix b/default.nix
index 9031a35..e1a4e45 100644
--- a/default.nix
+++ b/default.nix
@@ -210,7 +210,7 @@ rec
         pkgs.runCommand "niv_${cmd}_help" { buildInputs = [ niv ]; }
           "niv ${cmd} --help > $out"
       );
-      cmds = [ "add" "update" "drop" "init" "show" ];
+      cmds = [ "add" "update" "modify" "drop" "init" "show" ];
     in
       pkgs.lib.replaceStrings
         ([ "replace_niv_help" ] ++ (map (cmd: "replace_niv_${cmd}_help") cmds))
diff --git a/src/Niv/Cli.hs b/src/Niv/Cli.hs
index aa1aeeb..f13257d 100644
--- a/src/Niv/Cli.hs
+++ b/src/Niv/Cli.hs
@@ -399,7 +399,7 @@ parseCmdModify =
   where
     desc =
       [ Opts.fullDesc
-      , Opts.progDesc "Modify dependency"
+      , Opts.progDesc "Modify dependency attributes without performing an update"
       , Opts.headerDoc $ Just $
           "Examples:" Opts.<$$>
           "" Opts.<$$>