The price starts at $399 (£399, AU$649) for the GPS-only model, and $499 (£499, AU$799) for both GPS and cellular.
There are many varieties of new looks from which to choose.
One of the styles is a brushed-titanium finish.
The Apple Watch apps focus on user fitness and biometrics.
It also assists with health research.
The watch has an always-on display and an all-day, 18-hour battery life.
Additional features are a native compass and a decibel reader.
Apple announced that iPhone and Apple Watch users can soon share their health data with major health organizations to be part of several health studies.