This article analyses how firms build their capabilities for alliance portfolios. We investigate different solutions that are adopted across portfolio sizes, and whether the adoption of these solutions explains alliance portfolio performance. Our findings illustrate which solutions practitioners should consider implementing when expanding their alliance portfolio, and which can help enhance their portfolio performance. Our conclusions are based on a sample of 192 firms managing over 3,400 strategic alliances and seven expert interviews. We analyse the adoption of 14 distinct alliance practices in four solution categories. Our results reveal whether and when functional and staffing (e.g. alliance manager, alliance department), tool-based (e.g. intranet, codification of best practices), training (e.g. in-house, external training) and third party (e.g. consultant, mediators) solutions help firms transition successfully between small, medium, and large alliance portfolios, and to what extent they are associated with alliance success. Rules of engagement for successful alliance portfolio management are discussed.