Over the last 20 years in Australia the attitude of Government to policy evaluation has changed dramatically. Ministers (and Treasury officials) are no longer content to rely on anecdotes from agency heads as evidence that their programs are working. Rigorous evaluation is usually required, especially if the program is controversial or expensive. This is an encouraging development because it provides greater assurance that taxpayer funds are being wisely spent. Many of those responsible for fashioning or implementing new policies, however, though experts in their own field, have only a limited understanding of the circumstances in which rigorous evaluation is possible.