The Watch OS is the software that is found as the operating system of the Apple Watch which was created by Apple Inc. The system is quite similar to the original iOS system and there are similar features between the two systems. The Watch OS 4 is the fourth iteration of the software which sees many new developments in the system. There are many new updates that see users adapting to new functionality that makes the watch very favorable to use. This book will seek to explore the various features of the watchOS 4 operating system so the reader will be aware of what is available.