Monitoring applications define an important

class of applications used in wireless sensor networks.

In these applications the network perceives

the environment and searches for event

occurrences (phenomena) by sensing different

physical properties, such as temperature, humidity,

pressure, ambient light, movement, and presence

(for target tracking). In such cases the

location information of both phenomena and

nodes is usually required for tracking and correlation

purposes. In this work we summarize most

of the concepts related to localization systems for

WSNs as well as how to localize the nodes in

these networks (which allows the localization of

phenomena). By dividing the localization systems

into three distinct components — distance/angle

estimation, position computation, and localization

algorithm — besides providing a didactic

viewpoint, we show that these components can

be seen as subareas of the localization problem

that need to be analyzed and studied separately.