Organisations - including both corporations and start-ups - are usually established for a specific goal or purpose. Very rarely entrepreneurs want to build an organisation simply to have it. They want to accomplish something meaningful and important. Organisation’s purpose, more noble than to generate profits, is critical for its sustainability and for the impact it can have on its customers, employees and the society. We assess organisation accomplishments through its business performance or business effectiveness which should not be reduced to financial profitability. Organisation’s achievements can be assessed by the way it brings its noble purpose or vision closer to reality. This is also important from the point of view of the organisation’s sustainability. Business effectiveness is correlated with leadership effectiveness. Leadership Circle Profile methodology analyses leader’s effectiveness in relation to leader’s natural, protective or reactive tendencies, and creative competencies. Effective leaders have certain sets of both. The biggest impact on business effectiveness has not leadership effectiveness of individual leaders but, and this is extremely important, collective leadership effectiveness of the leadership team. I will explain why this is so important especially in modern organisations which are Complex Adaptive Systems. I will also analyse what it means to be a team - to be a good or effective leadership team. I will propose creation of a Deliberately Developmental Ecosystem (DDE) or Deliberately Developmental Organisation (DDO) as a way to build effective leadership teams. After describing the nature of DDE and DDO, I will explain why this is not an easy journey and what can help us to be successful on the way.