How to resume/continue file transfer over SSH/SCP

To recursively copy a directory's contents, continuing previously interrupted transfers, to/from a remote server via SSH/SCP, use rsync like this:
rsync --partial --progress -avz -e ssh <source> <destination>

where either <source> or <destination> can be a local path (eg. /directory/with/files/) or a remote path (eg. youruser@example.com:/new/directory/).