Higher-Dimensional Categories: an illustrated guide book by Eugenia Cheng, Aaron Lauda
Publisher: University of Sheffield 2004
Number of pages: 182
This work gives an explanatory introduction to various definitions of higher-dimensional category. The emphasis is on ideas rather than formalities; the aim is to shed light on the formalities by emphasizing the intuitions that lead there. To aid this, the tone is informal and there are copious pictures.
Mathematics Category Theory