Agent-based models (ABM) or individual-based models (IBM), as they are called in ecology and biology, are a widely used modeling approach when local interactions on the micro level are essential for the description of patterns on the macro level. This chapter is divided into four sections. In the first section, the history and definitions of ABMs in various research disciplines, namely computer science, social science, economics and ecology, are reviewed. This section closes with a discussion of similarities and differences in the different research fields and a discussion of current challenges in agentbased modeling. One of these difficulties is the lack of accepted standards for communication and programming. The second section refers to this point by a presentation of some widely used ABM libraries, namely Swarm, Mason, Repast and NetLogo and is followed by a more detailed description of NetLogo as a potential standard tool in ABM communication. In the last section extensions to NetLogo, developed by the authors of this chapter, are presented. This includes the MultiViewExtension, the R-Extension and the NetLogo plug-In for the Pygments syntax highlighter. The chapter closes with an outlook to further tools for NetLogo which aim at making NetLogo even more relevant as a standard tool in ABM.