Some interest groups, when referring to their participation in EU policy processes, summarize their experience thus: ‘We are more and more consulted but less and less heard’. While the governance concept in general, and EU multi-level governance in particular, argue for the inclusion of interest groups in the policy process, those groups’ statements prove that in reality the situation is different. The questions that must be answered, then, are: why does this happen, and where is the catch? This thesis examines the EU’s relationships with interest groups in general, and, in particular, the factors supporting and opposing NGOs’ and business groups’ successes and failures in influencing EU policies. I seek to answer the following questions: How does the organization of the EU political system assist or limit NGOs’ and business groups’ participation in the policy process? Does their position in policy networks have any influence on their input transposition? Does it affect the quality of their input? Can external factors to the policy processes themselves be a reason for lack of input implementation? I focus on three case studies. Firstly, as a background study, I examine the EU political system; subsequently, I analyze the EU Sustainable Development Policy and the EU Regulation on chemicals and their safe use (REACH) as particular examples of ‘on-the-ground’ cases. My main methodologies are process-tracing (including comparative content text analysis), social-network analysis, and interviews with key informants. The results are striking. The EU political environment does not appear to be as open as its supporters would like it to be perceived. Coalition-building proves to be the most efficient element of successful interest-group campaigns. The quality and independence of the input of interest groups is questionable. And finally, it emerges that external factors, which should be irrelevant, have a major influence – both positive and negative – on groups’ input transposition, depending on the situation.