Since the development of cuckoo search (CS) by Yang and Deb in 2009, CS has been applied in a diverse range of applications. This paper first outlines the key features of the algorithm and its variants, and then briefly summarizes the state-of-the-art developments in many applications. The opportunities for further research are also identified. 4th IEEE Conference on Soft Computing and Machine Learning (ISCMI2017), Mauritius, 23-24 Nov 2017