Coexistence is defined as "the ability of one system to perform a task in a given shared environment where other systems have an ability to perform their tasks and may or may not be using the same set of rules." This is more commonly described as the ability for 802.15.4-based wireless sensor network (WSN) systems to operate in the same band of frequency as other systems like Wi-Fi and Bluetooth.

Coexistence problems can occur when information transmitted by these different systems overlaps in time and frequency. Essentially, the transmissions "collide," and these collisions result in both systems suffering data loss because the transmitted information is no longer recoverable.

Early pioneers in radio technology struggled with these issues as various technologies evolved, but modern day RF techniques are well standardized to mitigate these issues. The 802.15.4 protocol, a physical layer protocol resulting from many years of collaborative work, was standardized by the Institute of Electrical and Electronic Engineers (IEEE). This organization is also responsible for the 802.11 (commonly called Wi-Fi) and 802.15.1 (referred to as Bluetooth) standards. These standards were all designed to coexist with one another and provide mechanisms to ensure that the RF spectrum can be safely shared.