It is a matter of course that each country in the large European Union presents specific characters and individual features of its own industrial environment. However, a common peculiarity can be recognized, evidenced by two numbers: the percentage of SMEs in any national industrial system, always close to 90% of the total number of enterprises, and the percentage of personnel employed in SMEs, greater than 60% of the active population. What can also be widely recognized in almost all European countries are the recent crises, which have affected SMEs, and the attempt by SMEs to counteract their difficult position by searching for agreements and cooperation. One type of reciprocal support SMEs looked for in a crisis was contracts with larger enterprises: this gave rise to supply chains. But often the desire of SMEs was to have collaborative links with other SMEs, operating in the same industrial sector and mainly located in the same region: this resulted in the rise of networks and districts. In the last decade, the European Commission has started to promote studies devoted solely to supporting these types of clustering. Some countries have also launched programs to finance SME aggregations, defining agencies for pushing the establishment of new SMEs groups. This chapter offers an outline of a number of different national situations, concerning the rise and, sometimes, the fall of SME clusters and networks. Obviously, the scope of this chapter is not to give an exhaustive presentation of the European situation of SME aggregations: it aims to force the reader to recognize similarities, weakness and strength aspects, and to apply these to an analysis of the SME aggregations performance.