In this chapter, the systematic analysis and literature of the existing routing protocols are discussed. The application-specific choice of the routing method is a primary challenge in a wireless sensor network or internet of things for efficient and reliable transmission of data. The reliable transmission of the data depends on various factors such as application, data generation rate, sampling rate, etc. The most commonly used routing is flat routing, also called data-centric routing. There are many other routing methods, e.g., hierarchical routing, location-based routing, energy-aware routing, multipath routing, etc. In this chapter, the discussion is divided into purely proactive and reactive routing methods or clustering-cum-routing advanced methods for all the different applications and needs. In the chapter, the network performance is optimized for the number of optimal clusters, the maximal throughput, and the lifetime. In addition, the comparative analysis of different routing and clustering protocols is also discussed in the chapter.