'Unconferences' are a non-traditional form of professional activity defined by the absence of many conventional conference structures. One example of the unconference model is the 'Edcamp,' a voluntary, participant-driven form of grassroots educator professional learning. More than 600 of these events have been held worldwide since the first in 2010. This exploratory study situates Edcamps in relationship to the literature on educator professional development and teacher collaboration, and reports on data gathered from 95 participants in an Edcamp in the United States. Respondents indicated diverse motivations for their Edcamp participation, including colleagues' recommendations, anticipated learning and the desire to network and collaborate. Respondents generally rated their Edcamp experiences highly, and overwhelmingly reported intentions to attend future Edcamps. The positive environment, participant autonomy and integration of technology were highlighted. Most participants, however, also identified ways in which their experiences could have been improved. The nature and topics of discussion, as well as challenges associated with Edcamp novices and technology, presented barriers to full participation. Implications of this research for educators, researchers and educational institutions are discussed.Keywords: professional learning; teacher collaboration; teacher learning; teacher community; teacher autonomy Introduction 'Unconferences' are voluntary, informal learning experiences that reject traditional conference structures such as a predetermined slate of speakers and sessions (Boule 2011). In 2010, a group of educators in the United States who had participated in a technology-focused unconference event subsequently organized the first Edcamp (Demski 2012). Hundreds of Edcamps have occurred in the intervening years. These experiences feature educators taking part in discussion-based sessions that are determined on the morning of the event. Edcamps typically exist outside school districts' formal professional development (PD) structures. Many educators beyond those who physically attend Edcamps have been exposed to the model by participants' active use of social media during events (Miles 2014). There is, however, almost no published, peer-reviewed research on Edcamps. Professional Development in Education, 2016 Vol. 42, No. 1, 78-99, http://dx.doi.org/10.1080/19415257.2015 Background Edcamps and other unconferences are based in part on the principles of 'Open Space Technology' (Owen 2008), a strategy for organizing meetings that has been used for more than 20 years in a variety of contexts. Open Space Technology emphasizes the ability of groups with a shared focus and an impetus for action to self-organize, collaborate and solve problems related to complex issues. Advance agendas, plans and materials are considered potentially counterproductive, as they may limit the engagement and collaboration of participants. The 'law of two feet' is also a key feature of Open Space Technology (Owen 2008, p. 95); this p...