Over the last forty years, the field of public economics has emerged as a modern successor to public finance. It has gained importance on the research agenda of economists and in the curricula of economics depa- ments. It has become a diversified field, rich in theoretical developments and substantive applications. Beyond the traditional concerns with t- ation or public goods, a number of new concerns have entered the scene, concerning for instance public sector pricing, the management of public firms, social security or federalism. A comprehensive presentation of the field extends nowadays beyond the scope of textbooks and requires access to a growing specialised literature. The present volume, collecting 22 papers published by Henry Tulkens over the period 1978–2003, is offered as an illustration of these new developments. The illustration has three dimensions: approach, s- ject matters and methods. Coming from a single author, admittedly assisted by 18 co-authors, the different papers are illustrative of an underlying general approach, which I like to label ‘‘operational public economics’’. With these simple words, I mean an approach under which issues in public economics are formulated so as to capture essential elements of actual situations. Ty- cally, this leads to theoretical models more complex than standard te- book formulations. It is then up to the public economist to extend the theory as needed to fit the situation.