diff --git a/doc/src/03100-lib-rt.md b/doc/src/03100-lib-rt.md
index 67e6f10d..3053adeb 100644
--- a/doc/src/03100-lib-rt.md
+++ b/doc/src/03100-lib-rt.md
@@ -9,3 +9,65 @@ and logging setup.
 The runtime library also provides helper functions for building a commandline
 interface.
 
+## Configuration file {#sec:librt:cfg}
+
+The runtime library SHOULD read the configuration file, if it can be found.
+If the configuration file cannot be found, the following variables are set to
+their default values as shown in @tbl:librt:cfg:defaultvalues.
+
+| Variable       | Value                |
+| :------------- | :------------------- |
+| verbosity      | false                |
+| debugging      | false                |
+| store location | `$HOME/.imag/store/` |
+
+Table: Default values for configuration if configuration file unavailable
+{#tbl:librt:cfg:defaultvalues}
+
+### Location of the configuration file {#sec:librt:cfg:location}
+
+For the configuration file is searched at the following locations:
+
+1. Path: `$HOME/.imag/config`
+1. Path: `$HOME/.imag/config.toml`
+1. Path: `$HOME/.imag/imagrc`
+1. Path: `$HOME/.imag/imagrc.toml`
+1. Path: `$XDG_CONFIG_DIR/imag/config`
+1. Path: `$XDG_CONFIG_DIR/imag/config.toml`
+1. Path: `$XDG_CONFIG_DIR/imag/imagrc`
+1. Path: `$XDG_CONFIG_DIR/imag/imagrc.toml`
+1. Path in the environment variable `$IMAG_CONFIG`
+
+If neither of these configuration files are found, the program MUST USE the
+default values for the minimum required variables
+(@tbl:librt:cfg:defaultvalues).
+
+### Contents of the configuration file {#sec:librt:cfg:contents}
+
+The contents of the configuration file MUST BE encoded in Unicode UTF-8.
+The contents of the configuration file are structured as TOML, regardless of the
+file extension.
+
+The configuration file contains several sections:
+
+1. The `base` section, which contains basic variables
+   (@tbl:librt:cfg:contents:base)
+1. The `modules` section, which contains a section for each module.
+1. The `store` section, which contains configuration on the behaviour of the
+   store (@tbl:librt:cfg:contents:store)
+
+| Variable       | Type    |
+| :------------- | :------ |
+| verbosity      | boolean |
+| debugging      | boolean |
+| store location | Path    |
+
+Table: "Base" variables in the configuration file {#tbl:librt:cfg:contents:base}
+
+
+| Variable  | Type    | Meaning                                          |
+| :-------- | :------ | :----------------------------------------------- |
+| git-vcs   | boolean | Whether the store is version controlled with git |
+
+Table: "store" variables in the configuration file {#tbl:librt:cfg:contents:store}
+