The book "Abstract and Concrete Categories (The Joy of Cats)" by Jiri Adamek, Horst Herrlich and George E. Strecker, though out print for some time, is available again via the internet address http://katmat.math.uni-bremen.de/acc This is an open-access publication and can be freely used and distributed. It contains corrections and small improvements and some new sketches by Marcel Erne. We are grateful to Christof Schubert whose skill and untiring effort made this possible. Take a look, enjoy, and let others know!