The development of digital collections deeply examines the roles and practices of library professionals. In this article, we will address the question of those new collections from the standpoint of both the professionals, and the users. We propose an analysis focusing on questions of choice and selection, of organization and classification and lastly, on services rendered to users. This analysis will draw on three characteristics of digital collections as being unstable, near-boundless and their heterogeneity. These three dimensions compel librarians to reconsider their position and role regarding the intellectual and organizational development of collections. We will also address the reception of these collections from the user's perspective. In fact, today's users are often confronted to offers that resemble the structure found in libraries. The membership model leads to a lump-sum scheme payment for access, versus ownership, to a wide bundle of digital resources, in constant evolution. The very rapid development of this type of model for most cultural industries, leads individuals, thus library users, to develop an apprehensive and exploitative form of digital literacy of those collections. This goes through innovative interfaces of exploration and mediation in which we find some recurring procedures, such as endless stacks and algorithmic recommendation. We conclude this article with a brief presentation of ongoing projects facing these issues and the necessity to roll out an in-depth reflection on the position of libraries in this new ecosystem.