diff --git a/README.md b/README.md
index 7862081..e6d7085 100644
--- a/README.md
+++ b/README.md
@@ -5,19 +5,20 @@ portzap is a utility for staying up to date with the
 The utility stores a transient copy of the ports tree in `/home/_portzap/ports/`.
 The transient copy can be created, and updated by an unprivileged user account
 who is a member of the `_portzap` group. The transient copy can then be installed
-into the `/usr/ports` directory by root.
+into the `/usr/ports/` directory by root.
 
 ## Usage
 
 * `portzap clone` <br>
-  This command clones HardenedBSD's ports tree into `/home/_portzap/ports`.
+  This command clones HardenedBSD's ports tree into `/home/_portzap/ports/`.
 
 * `portzap pull` <br>
-  This command pulls updates into `/home/_portzap/ports`.
+  This command pulls updates into `/home/_portzap/ports/`.
 
 * `portzap install` <br>
   This command should be run as root. <br>
-  The command installs `/home/_portzap/ports` into `/usr/ports`.
+  The command installs `/home/_portzap/ports/` into `/usr/ports/`. <br>
+  After the first installation, future installations try to save time by being incremental.
 
 ## Sources
 
diff --git a/bin/portzap b/bin/portzap
index 9531b89..7a8ce29 100755
--- a/bin/portzap
+++ b/bin/portzap
@@ -6,6 +6,7 @@
 # Configuration
 ports_url="https://git.hardenedbsd.org/hardenedbsd/ports.git"
 ports_dir="/usr/ports/"
+portzap_rev="$ports_dir/.portzap_last_rev"
 portzap_dir="/home/_portzap/ports"
 libexec_dir=$(realpath $(dirname $0)/../libexec/portzap/)
 
@@ -17,6 +18,9 @@ pull_mask=007
 
 ##
 # Utils
+. $libexec_dir/functions/perms.sh
+. $libexec_dir/functions/fs.sh
+. $libexec_dir/functions/git.sh
 exit_on_missing_deps() {
     deps=$1
     for dep in $deps; do
@@ -28,24 +32,6 @@ exit_on_missing_deps() {
     done
 }
 
-has_portzap_access() {
-    groups=$(id -Gn)
-    in_group=1
-    for g in $groups; do
-        if [ $g = "_portzap" ];
-        then
-            in_group=0
-        fi
-    done
-    return $in_group
-}
-
-user_is_not_root() {
-    user_id=$(id -u)
-    result=$(test $user_id -ne "0")
-    return $result
-}
-
 ##
 # Commands
 help() {
@@ -98,16 +84,35 @@ install() {
         exit 1
     fi
 
+    echo "Please wait..."
     cd $portzap_dir
-    find -s . -maxdepth 1 -type f \
-        \( -not -name ".gitignore" \) \
-        \( -not -name ".arcconfig" \) \
-        -exec $libexec_dir/install-file $ports_dir {} +
-    find -s . -maxdepth 1 -type d \
-         \( -not -name "." \) \
-         \( -not -name ".git" \) \
-         \( -not -name ".hooks" \) \
-         -exec $libexec_dir/install-directory $ports_dir $libexec_dir {} +
+    if [ -e "$portzap_rev" ]; then
+        rev=$(cat $portzap_rev)
+        port_dirs=$(modified_ports $rev)
+        rm_files=$(git diff --name-only --diff-filter=D $rev..HEAD)
+        for file in $rm_files; do
+            rm $ports_dir/$file
+        done
+        for dir in $port_dirs; do
+            if [ -f "$dir" ]; then
+                $libexec_dir/install-file $ports_dir $dir
+            else
+                $libexec_dir/install-directory $ports_dir $libexec_dir $dir
+            fi
+        done
+    else
+        find -s . -maxdepth 1 -type f \
+            \( -not -name ".gitignore" \) \
+            \( -not -name ".arcconfig" \) \
+            -exec $libexec_dir/install-file $ports_dir {} +
+        find -s . -maxdepth 1 -type d \
+            \( -not -name "." \) \
+            \( -not -name ".git" \) \
+            \( -not -name ".hooks" \) \
+            -exec $libexec_dir/install-directory $ports_dir $libexec_dir {} +
+    fi
+    echo $(git rev-parse HEAD) > $portzap_rev
+    echo "Done."
 }
 
 case $1 in
diff --git a/libexec/portzap/functions/fs.sh b/libexec/portzap/functions/fs.sh
new file mode 100755
index 0000000..db4d188
--- /dev/null
+++ b/libexec/portzap/functions/fs.sh
@@ -0,0 +1,24 @@
+#!/bin/sh
+
+##
+# Returns the depth of a path
+port_depth() {
+    p=$1
+    result=$(echo $p | tr '/' '\n' | grep . | wc -l)
+    return $result
+}
+
+##
+# Returns the entry point for a port relative to /usr/ports
+# (eg: ./ftp/curl/)
+port_dirname() {
+    p=$1
+    port_depth "$p"
+    depth=$?
+    if [ $depth -gt 2 ]; then
+        p=$(dirname $p)
+        port_dirname "$p"
+    else
+        echo $p
+    fi
+}
diff --git a/libexec/portzap/functions/git.sh b/libexec/portzap/functions/git.sh
new file mode 100644
index 0000000..79715f1
--- /dev/null
+++ b/libexec/portzap/functions/git.sh
@@ -0,0 +1,11 @@
+##
+# Returns a list of new, and modified files between two points / commits.
+modified_ports() {
+    rev=$1
+    files=$(git diff --name-only --diff-filter=AM $rev..HEAD)
+    for file in $files; do
+        dirs="$dirs $(port_dirname $file)"
+    done
+    dirs=$(echo $dirs | tr ' ' '\n' | uniq)
+    echo $dirs
+}
diff --git a/libexec/portzap/functions/perms.sh b/libexec/portzap/functions/perms.sh
new file mode 100644
index 0000000..2ba718e
--- /dev/null
+++ b/libexec/portzap/functions/perms.sh
@@ -0,0 +1,21 @@
+##
+# Returns true when current user is in _portzap group
+has_portzap_access() {
+    groups=$(id -Gn)
+    in_group=1
+    for g in $groups; do
+        if [ $g = "_portzap" ];
+        then
+            in_group=0
+        fi
+    done
+    return $in_group
+}
+
+##
+# Returns true when current user is root
+user_is_not_root() {
+    user_id=$(id -u)
+    result=$(test $user_id -ne "0")
+    return $result
+}