This book, written in 1977, brought together for the first time current knowledge of plants that might be relevant to understanding their population biology. "This monumental volume did more than summarize the state of plant biology; ...it linked the conceptual and theoretical developments in population ecology, mostly derived from the study of animals, with field observations and experimental evidence of population regulation and life history evolution in plants. ""The field of population biology was already well established in the 1960s although with a clear zoocentric emphasis. However, it is because of Harper's work that the field experienced a veritable explosion, reached maturity and became a mainstream scientific endeavour worldwide. This field is so vast now that it would be pointless, if not impossible, for someone to summarise it. It is precisely because of this that PBP is as relevant now as it was in 1977. John Harper's style of highlighting unanswered questions and the limitations of both theory and empirical evidence served and still serves as foundation for research agendas worldwide. Much remains to be done in this field and this alone makes PBP an essential element in the library of every student/researcher of population biology, whether interested in plants or animals."From the "Preface to the 2010 Printing" written by José Sarukhán, Rodolfo Dirzo and Miguel Franco.