The use of Agile methodologies is gaining popularity in the information technology (IT) project market as a successful alternative to traditional practices and methodologies, which are often not appropriate to the scenario of change and creative work of IT projects, and this way have been blamed for the high rate of failure in projects that apply them in that area. However, the practice of Agile values by IT teams, essential for the successful use of Agile methodologies and frameworks, may represent a paradigm shift of difficult achievement for most teams. This study aimed to identify and analyze the main factors facilitating and main factors hindering the practice of Agile values by IT system development teams, from the perspective of members and leaders of these teams, and the conditions that influence the manifestation of these factors. To this end, we performed a phenomenographic study, using semi-structured interviews with members and team leaders of Agile IT system development teams from Brazil. The critical factors, once identified, were classified and analyzed using theoretical references of Business Administration with an emphasis on the theory of Lean Production, complemented by theories of self-managed work teams, motivation at work, customer relations and customer participation on service production.