Monitoring, as defined by Elzinga and others (1998), is 'the collection and analysis of repeated observations or measurements to evaluate changes in condition and progress towards meeting a management objective.' Analyses of monitoring data may indicate that a project is meeting land management goals, or it may indicate that goals are not being met and management methods need to be adapted to reach them. Monitoring is an essential step in adaptive management (Chong and others 2006). For many federal agencies, monitoring is required by Agency or Congressional mandates (Elzinga and others 1998). Monitoring can be qualitative or quantitative and can be applied with varying levels of rigor (see Elzinga and others 1998 for a complete discussion). Monitoring with a high level of rigor is essential for change to be detected and for cause and effect relationships to be inferred. In other words, a high level of rigor is needed for monitoring to produce defensible results that are useful for management decisions. In the rest of this chapter, when I use the term 'monitoring,' I mean monitoring with a high level of rigor. Monitoring is essential for understanding the relationship between fire and invasive species, whether documenting new invaders following fire, postfire changes in established nonnative populations, recovery of native plant communities after wildfire (fig. 15-1), or efficacy of prescribed fire in controlling nonnative plant species. Monitoring can be used to detect change between sampling periods (before and after fire) or between treatments (burned and unburned areas), and it provides quantitative data for statistically analyzing the probability that the observed differences are due to chance. Statistics provides an objective and defensible means of evaluating the relationship between invasives and fire; it provides 'high quality information' as described in chapter 12. However, statistical significance does not necessarily imply biological significance (see 'Statistical Analysis' page 285). This chapter is not a guide on how to monitor nonnative invasive plants. Many such guides are available, some in textbooks and others in agency manuals, which are referenced throughout the chapter. Instead of providing how-to instructions, this chapter (1) identifies common elements of effective monitoring programs and suggests sources for additional information on those elements, (2) provides examples of how decisions on monitoring design can affect results and interpretation of the results, and (3) stresses the importance of integrating vegetation, fire behavior, and fire effects monitoring to better understand the impact of fire on nonnative, invasive species.