This paper draws on the experiences of portfolio entrepreneurs and develops new insights into this important mode of business development. Portfolio entrepreneurs own and manage multiple businesses simultaneously, providing an alternative growth process and the prospect of enduring entrepreneurship. Previous research has focused on either the genealogy of businesses in a portfolio or the human capital attributes that determine who becomes a portfolio entrepreneur and how they perform relative to other types of entrepreneurs. Key issues involving the structure, strategy and management of portfolios need further exploration and development. This multiple-case study conducted in New Zealand features eleven entrepreneurs with portfolios of different ages and sizes, each reflecting a series of opportunistic responses to different situations. Our results show that some entrepreneurs use structure as an internal seedbed to spawn new ventures, others seek opportunities to acquire more businesses, while some use both means to build and maintain their business groups. Structure is the dominant construct, providing a flexible canvas upon which entrepreneurs enact growth ambitions by creating and re-creating their portfolios over time. We found no evidence of portfolio-level decision making or performance measurement with the lead entrepreneur’s attention largely focused at the business unit level.