This document reviews various techniques for preserving privacy in wireless sensor networks. It discusses the challenges of privacy preservation in WSNs due to their unique characteristics like resource constraints and topological constraints. It then summarizes several key techniques explored in research for preserving data privacy, source location privacy, sink location privacy and network privacy. These techniques include clustering-based approaches, random walk-based approaches and mixing-based approaches. The document concludes that while progress has been made, more research is still needed in areas like peer-to-peer network privacy preservation.