If you are looking for an introduction to agroecology and/or a textbook for a course on sustainable agriculture, "Agroecology: Science and Politics" (2017) by Rosset and Altieri is it. This book is written by leading experts, activists, and advocates (which motivates the book), for students this might be read in combination with a parallel book offering a different perspective for comparative purposes. As a stand alone book it is also excellent, concise (for a topic that could be complicated), and readable at 146 pages. Chapters cover the principles, history, current directions, evidence, examples of scaling, and politics. Examples given are concrete, with references for follow up and deeper engagement. A key point that the authors make throughout is that agroecology is political. Very useful introductory book. One of the authors has put the book online here.
A few notes:
"Agroecology combines indigenous knowledge systems about soils, plants and so on with disciplines from modern ecological and agricultural science. By promoting a dialogue of wisdoms and integrating elements of modern science and ethno-science, a series of principles emerge, which when applied in a particular region take different technological forms depending on the socio-economic, cultural and environmental context." (p. 9)
"Most analysts today agree that increasing food production will be a necessary but not a suﬃcient condition to prevent future hunger around the world. Hunger results from underlying inequities in the dominant capitalist system that deprive poor people of economic opportunity, access to food and land and other resources vital for a secure livelihood (Lappé, Collins and Rosset 1998). Focusing narrowly on increasing food production cannot alleviate hunger because it fails to alter the tightly concentrated distribution of economic power that determines who can buy food or have access to seeds, water and land to produce it." (p. 68)
"While most agroecology research to date has emphasized natural science, these results point to the need to prioritize social science approaches and self-study by rural movements, to draw systematic lessons from their successful experiences. This can produce the information and principles needed to design new collective processes." (p. 114)