Wireless sensor networks (WSNs) allow innovative applications and involve non-conventional models for the design of procedures owing to some limitations. Due to the necessity for low device complication and low consumption of energy, an appropriate equilibrium among communication and signal processing abilities should be instituted. This stimulates an enormous effort in research actions, standardisation procedure, as well as manufacturing investments on this aspect since the preceding years. Therefore, this chapter aims at presenting a summary of WSNs machineries, foremost applications and values, structures in WSNs project, and the developments drawn from some evidence and meta-data-based survey and assessments. Precisely, some applications, such as those based on ecological monitoring, and design approaches that emphasise a real implementation are discussed briefly. The trends and conceivable developments are outlined. Emphasis is given to “the Institute of Electrical and Electronics Engineers (IEEE) 802.15.4 technology” that enables several applications of WSNs. Hence, it is anticipated that this chapter would serve as an introductory aspect on the applications and challenges of WSNs for persons interested in WSNs.