The OpenSSH suite provides secure remote access and file transfer. Since its initial release, it has grown to become the most widely used implementation of the SSH protocol. During the first ten years of its existence, ssh has largely replaced older corresponding unencrypted tools and protocols. The OpenSSH client is included by default in most operating system distributions, including OS X, Linux, BSD and Solaris. Any day you use the Internet, you are using and relying on hundreds if not thousands of machines operated and maintained using OpenSSH. A survey in 2008 showed that of the SSH servers found running, just over 80% were OpenSSH.  Even with the advent of the Internet of Things and the increased use of IPv6, a cursory search of Shodan  for SSH-2.0 services on port 22 in April 2017 showed 56% of responding IPv4 addresses running OpenSSH. 
OpenSSH was first released towards the end of 1999. It is the latest step in a very long and useful history of networked computing, remote access and telecommuting.
This book is for fellow users of OpenSSH to help them save effort and time through using OpenSSH, and especially SFTP, where it makes sense to use it.