Researchers interested in exploring the role played, within policy networks, by organizations representing collective and/or public interests are faced with an array of options which is as impressive as potentially confusing. They may concentrate on the organizations considered most influential in a certain policy domain (e.g. Laumann and Knoke, 1987), or they may look at the entire field of organizations operating on a certain issue or set of linked issues (e.g. Diani, 1995); they may focus on organizations that are closest to the model of the social movement (e.g. Amenta et al., 1992) or, instead, pay attention to public interest groups in the broadest sense, sometimes without even acknowledging any meaningful difference between social movement organizations and interest groups (e.g. Burstein and Linton, 2002).

While each of these strategies may offer valuable insights, it is important to be explicit regarding the types of actors whose role in policy-making we want to explore, and on the relations that they entertain to other actors with similar agendas. Although their internal structure may substantially differ, organizations representing public interests are not usually strong enough to be able to operate entirely on their own. In most cases, they are involved in some kind of alliance and cooperation with cognate organizations. Even if they operate mostly independently, they are nonetheless located within broader organizational fields. This has some important consequences for the analysis of policy networks.