* math overflow, Relation between monads, operads and algebraic theories, [web](http://mathoverflow.net/questions/66641/relation-between-monads-operads-and-algebraic-theories) * Max Kelly, on the operads of J.P. May * Tom Leinster, Higher Operads Higher Categories * Nishizawa and Power, Lawvere theories enriched over a general base, JPAA 213, 2009 * Linton's An outline of functorial semantics, LNM 80, 1969 * Cruttwell and Shulman's A unified framework for generalized multicategories, TAC 24(21), 2010, * Clemens Berger, Paul-André Melliès, Mark Weber - Monads with arities and their associated theories [arXiv:1101.3064 [math.CT]](http://arxiv.org/abs/1101.3064) * Martin Hyland, John Power - The category theoretic understanding of universal algebra: Lawvere theories and monads - Electronic Notes in Theoretical Computer Science [pdf](https://www.dpmms.cam.ac.uk/~martin/Research/Publications/2007/hp07.pdf) * Martin Hyland, classical lambda calculus in modern dress, [arXiv:1211.5762 [math.CT]](http://arxiv.org/abs/1211.5762)