 <p>CATransaction works on Core Animation layer animations. CATransaction is cross-platform between iOS and Mac OS.</p> <p>NSAnimationContext works with an NSAnimationContext. It's Mac OS specific.</p> <p>(The NS animation stuff is Mac-only, and the UIView animation stuff is iOS only.)</p> <p>I work in iOS more than Mac OS these days, and I always look for cross-platform ways to do things. </p> <p>CAAnimation, CALayer, CAAnimationGroup, etc, are nearly identical between Mac and iOS. There are some differences (e.g. quicktime layers are not supported in iOS, Core Image support is more limited in iOS, etc.) but CA stuff is more alike than different.</p>