Internet usage has dramatically transformed from host-centric end-to-end communication to content retrieval. In order to adapt to this change, several new information/content centric networking (ICN) architectures have been proposed. One common and important feature of these architectures is to leverage built-in network caches to improve the transmission efficiency of receiver-driven content retrieval and network resource utilization. Compared with traditional Web cache and CDN cache systems, ICN cache takes on several new characteristics: Transparency, ubiquity, and fine granularity, which put new challenges on the modeling, understanding and optimization of the networked cache system. In this paper, new features of ICN as well as their ensuing challenges are introduced, mechanisms to optimize the performance of cache network are analyzed and compared from various angles, and analytical models for the cache system are also presented. The study concludes with a discussion on some key issues and future research directions.