diff --git a/README.md b/README.md
index 627e760..70532ea 100644
--- a/README.md
+++ b/README.md
@@ -7,10 +7,10 @@ Original sources are downloaded from https://landing.google.com/sre/books
 # Books
 
 ## Site Reliability Engineering
-<img src="sre-book.jpg" width="320" alt="sre-book" >
+<img src="cover/sre-book.jpg" width="320" alt="site reliability engineering cover" >
 
 ## The Site Reliability Workbook
-<img src="workbook.jpg" width="320" alt="srw-book" >
+<img src="cover/workbook.jpg" width="320" alt="the site reliability workbook cover" >
 
 # Build
 
@@ -20,8 +20,13 @@ Requirements:
 
 -   Docker
 
+You can generate either of books using `BOOK_SLUG` variable.
+
+Available values for `BOOK_SLUG`:
+  - `sre_book` Site Reliability Engineering.
+
 ```
-$ docker run --rm --volume "$(pwd):/output" captn3m0/google-sre-ebook:latest
+$ docker run --rm --volume "$(pwd):/output" captn3m0/google-sre-ebook:latest -e BOOK_SLUG='sre_book'
 ```
 
 -   You should see the final EPUB/MOBI/PDF files in the `output` directory after the above runs.
@@ -32,7 +37,7 @@ $ docker run --rm --volume "$(pwd):/output" captn3m0/google-sre-ebook:latest
 ```
 $ mkdir /tmp/sreoutput
 $ chcon -Rt svirt_sandbox_file_t /tmp/sreoutput
-$ docker run --rm --volume "/tmp/sreoutput:/output" captn3m0/google-sre-ebook:latest
+$ docker run --rm --volume "/tmp/sreoutput:/output" captn3m0/google-sre-ebook:latest -e BOOK_SLUG='sre_book'
 ```
 
 The build for the above Docker image can be audited at <https://cloud.docker.com/swarm/captn3m0/repository/docker/captn3m0/google-sre-ebook/builds>.
@@ -52,7 +57,7 @@ Requirements:
 
 # Known Issues
 
--   metadata.xml is not complete. There are just too many authors
+-   metadata is not complete. There are just too many authors
 -   Foreword/Preface is not part of the index
 
 # LICENSE
diff --git a/books.sh b/books.sh
new file mode 100644
index 0000000..f09d220
--- /dev/null
+++ b/books.sh
@@ -0,0 +1,15 @@
+# Google SRE Books.
+declare -A BOOKS
+BOOKS=(
+
+    # Site Reliability Engineering
+    ["SRE_BOOK"]=$(
+        echo '
+            BOOK_NAME=sre-book
+            BOOK_NAME_FULL=Site Reliability Engineering
+            BOOK_FILE=google-sre-book
+            BOOK_TOC_URL=https://landing.google.com/sre/sre-book/toc/index.html
+        '
+    )
+
+)
diff --git a/bootstrap.sh b/bootstrap.sh
index 2aa6b78..f27bab8 100755
--- a/bootstrap.sh
+++ b/bootstrap.sh
@@ -1,14 +1,15 @@
 #!/bin/bash
 set -euo pipefail
+
+# Get book details.
+source books.sh
+export ${BOOKS[${BOOK_SLUG^^}]}
+
+# Common vars.
+IMGS_DOMAIN="lh3.googleusercontent.com"
 IFS=$'\n\t'
 
-# Vars.
-export BOOK_NAME="sre-book"
-export BOOK_NAME_FULL="Site Reliability Engineering"
-BOOK_FILE="google-${BOOK_NAME}"
-TOC_URL="https://landing.google.com/sre/${BOOK_NAME}/toc/index.html"
-IMGS_DOMAIN="lh3.googleusercontent.com"
-
+#
 # Make sure that links are relative \
 # # Remove the /sre/ directories
 # Save stuff in html/ directory
@@ -27,7 +28,7 @@ wget \
     --mirror                \
     --no-verbose            \
     --recursive             \
-    --domains=${IMGS_DOMAIN},landing.google.com ${TOC_URL}
+    --domains=${IMGS_DOMAIN},landing.google.com ${BOOK_TOC_URL}
 
 #
 MODE=${1:-}
@@ -36,6 +37,7 @@ if [ "$MODE" != "docker" ];then
     bundle install
 fi
 
+#
 # Add extension to files.
 # That because `pandoc` cannot generate the right `mime type` without the extension.
 # https://github.com/captn3m0/google-sre-ebook/issues/19
@@ -52,19 +54,25 @@ for FILE_NAME_FULL in ${IMGS_FILES}; do
 
 done
 
+#
+# Generate epub from html.
 bundle exec ruby generate.rb
 pushd html/landing.google.com/sre/${BOOK_NAME}/toc
-pandoc --from=html --to=epub \
-    --output=../../../../../${BOOK_FILE}.epub \
-    --epub-metadata=../../../../../${BOOK_NAME}.xml \
-    --epub-cover-image=../../../../../${BOOK_NAME}.jpg \
+pandoc --from=html --to=epub                           \
+    --output=../../../../../${BOOK_FILE}.epub          \
+    --epub-metadata=../../../../../metadata/${BOOK_NAME}.xml    \
+    --epub-cover-image=../../../../../cover/${BOOK_NAME}.jpg \
     complete.html
 popd
 
+#
+# Generate other format from epub.
 for EXTENSION in mobi pdf; do
     ebook-convert ${BOOK_FILE}.epub ${BOOK_FILE}.${EXTENSION}
 done
 
+#
+# If it works inside docker.
 if [ "$1"=="docker" ]; then
     chown -v $(id -u):$(id -g) ${BOOK_FILE}.*
     mv -f ${BOOK_FILE}.* /output
diff --git a/sre-book.jpg b/cover/sre-book.jpg
similarity index 100%
rename from sre-book.jpg
rename to cover/sre-book.jpg
diff --git a/workbook.jpg b/cover/workbook.jpg
similarity index 100%
rename from workbook.jpg
rename to cover/workbook.jpg
diff --git a/sre-book.xml b/metadata/sre-book.xml
similarity index 100%
rename from sre-book.xml
rename to metadata/sre-book.xml