“Contemporary Druidry: A Historical and Ethnographic Study,” by Michael T. Cooper, is an academic study of modern Druidry, written by a non-Druid, associate professor of Religion and Contemporary Culture, at Trinity Graduate School in Deerfield, IL.
The book is divided into two main parts: a brief overview of the history of Druidry, and an ethnographic study, based on a combination of field observations and interviews conducted with a rather small sampling of 56 practicing Druids, primarily members of ADF (Ár nDraíocht Féin), OBOD (Order of Bards, Ovates, and Druids), but also including 7 members of the LAW (Loyal Arthurian Warband.
As you might expect from an academic, the volume is well annotated, and filled with citations. It is also highly readable, as academic writing goes. The areas of inquiry for this study were limited to the general topics of Druidic perspectives on the meaning of life, Druidic interpretations of death, well-being, and misfortune, and Druidic approaches to seeking guidance, and relating to the unknown. He also includes chapters on the relationship between (some) contemporary Druids and Stonehenge, and the pathways to conversion from other religious paths to Druidry.
The weakness of the study primarily stems from self-selection and sampling biases. Cooper admits that his access to sources was limited. He was able to survey and interview a few senior Druids in each of the three aforementioned organizations, who were willing to speak to an outsider. A few of those sources invited him to observe their public rituals, after which Cooper spoke with a few more participants, whom he met at those rituals. Given the diversity of Druidic beliefs and practices represented by the various Druid groups, groves, and teaching organizations scattered about the globe, and given the differences in perspective between those Druids who feel comfortable being open about their beliefs and practices and those who must remain private about their beliefs in order to avoid discriminatory retaliation, or worse, and given the exclusion from the study of solitary Druids, and Druids of other Druidry group affiliations, the results of this study are of limited value as a general study of Contemporary Druidry.
It is worth a glance, as part of a broad literature survey on Druidry, but it is not a comprehensive, stand-alone reference.