diff --git a/README.md b/README.md
index 0ede05d1..810031bb 100644
--- a/README.md
+++ b/README.md
@@ -79,6 +79,21 @@ uncompressed cloud image and about 20% of that for working files.
 
 \* As reported by /proc/meminfo MemTotal
 
+Caches and offline mode
+=======================
+
+Since retrieving and transforming operating system image files, git
+repositories, Python or Ruby packages, and so on can be a significant overhead,
+we cache many of the inputs to the build process in ~/.cache/image-create/. The
+writing an element documention describes the interface within
+disk-image-builder for caching. When invoking disk-image-builder the --offline
+option will instruct disk-image-builder to not refresh cached resources.
+
+Note that we don't maintain operating system package caches, instead depending
+on your local infrastructure (e.g. Squid cache, or an APT or Yum proxy) to 
+facilitate caching of that layer, so you need to arrange independently for
+offline mode.
+
 Design
 ======
 
@@ -222,6 +237,14 @@ Ramdisk elements support the following files in their element directories:
 
 * udev.d : udev rules files that will be copied into the ramdisk.
 
+Global image-build variables
+----------------------------
+
+* DIB\_OFFLINE : this is always set. When not empty, any operations that
+  perform remote data access should avoid it if possible. If not possible
+  the operation should still be attempted as the user may have an external
+  cache able to keep the operation functional.
+
 Structure of an element
 -----------------------
 
diff --git a/bin/disk-image-create b/bin/disk-image-create
index 3c2908c8..9e0dd378 100755
--- a/bin/disk-image-create
+++ b/bin/disk-image-create
@@ -43,6 +43,7 @@ function show_options () {
     echo "    -u -- uncompressed; do not compress the image - larger but faster"
     echo "    -c -- clear environment before starting work"
     echo "    --no-tmpfs -- do not use tmpfs to speed image build"
+    echo "    --offline -- do not update cached resources"
     if [ "$IS_RAMDISK" == "0" ]; then
         echo "    -n skip the default inclusion of the 'base' element"
         echo "    -p package[,package,package] -- list of packages to install in the image"
@@ -71,6 +72,7 @@ while true ; do
         -n) shift; export SKIP_BASE="1";;
         -p) IFS="," read -a INSTALL_PACKAGES <<< "$2"; export INSTALL_PACKAGES ; shift 2 ;;
         --no-tmpfs) shift; export DIB_NO_TMPFS=1;;
+        --offline) shift; export DIB_OFFLINE=1;;
         --) shift ; break ;;
         *) echo "Internal error!" ; exit 1 ;;
     esac
diff --git a/lib/common-defaults b/lib/common-defaults
index dc955000..23aa0acc 100644
--- a/lib/common-defaults
+++ b/lib/common-defaults
@@ -39,3 +39,4 @@ export DIB_NO_TMPFS=${DIB_NO_TMPFS:-0}
 _BASE_ELEMENT_DIR=$(dirname $0)/../elements
 ELEMENTS_PATH=${ELEMENTS_PATH:+"$ELEMENTS_PATH:$_BASE_ELEMENT_DIR"}
 export ELEMENTS_PATH=${ELEMENTS_PATH:-$_BASE_ELEMENT_DIR}
+export DIB_OFFLINE=''