This comprehensive chapter discusses the historic evolution, forms, and advancements of sound navigation and ranging (SONAR) sensors. Straddling from its start during World War I to its current advanced capabilities, the chapter highlights how SONAR technology has transmuted from basic acoustic hearing devices to erudite systems critical for underwater navigation, research, defense, and environmental conservation. It examines various types of modern SONAR sensors, including single-beam, multibeam, side-scan, forward-looking, Doppler, and synthetic aperture SONAR, clarifying their varied applications in underwater exploration, mapping, object detection, and current measurement. Furthermore, the chapter discusses the continuous innovations driving SONAR technology forward, emphasizing the integration of artificial intelligence, advancements in signal processing, and the potential for underwater communication networks. It underlines the concerted exertions among academia, industry, and government entities as key issues in pushing research and development in this field. The chapter also highlights the role of SONAR technology in untying the secrecies of the oceans, supporting scientific findings, endorsing safe navigation, contributing to environmental conservation, and nurturing advancements across various industries reliant on underwater exploration.