The problem of localization in a wireless sensor network has received considerable interest from researchers in the recent past. In this chapter, an extensive survey of the schemes proposed by different researchers from different perspectives is presented. The localization schemes are classified into different categories based on the strategies and schemes adopted. The major categories of localization schemes described are range-based, range-free, anchor-based, anchor-free, and directional localization. The major technique behind each localization scheme is discussed, and its relative merits and demerits are pointed out. The techniques in each category are compared, and their salient features are described.