This book described a set of procedures and generic factors that are said to remedy deficiencies in team decision making. How confident can we be of the validity of this claim? This chapter summarises the evidence for effectiveness of team decision support. We start by reviewing the use of approaches in practice drawing from published surveys, academic reviews, and case studies. Second, we bring together claims on products generated and impact created by team support procedures. This is followed by an examination of the evidence supporting or questioning the actual achievement of the products and impacts claimed by approaches. The evidence for effectiveness is growing. In particular, the impact on cognitive change (new knowledge) and alignment (consensus) is now shown in several studies in real-world settings, using a pretest–posttest design. However, several outstanding questions remain. Finally, we critically reflect on our findings and discuss what in our view are the most pressing issues in advancing research on effectiveness of team decision support approaches. A central issue is that while there is ample research on divergent processes, procedures that are effective in convergence deserve to be studied in more depth.