The ACL 2018 Workshop on Representation Learning for NLP (RepL4NLP) takes place on Friday, July 20, 2018 in Melbourne, Australia, immediately following the 56th Annual Meeting of the Association for Computational Linguistics (ACL). The workshop is generously sponsored by Facebook, Salesforce, ASAPP, DeepMind, Microsoft Research, and Naver. Repl4NLP is organised by Isabelle Augenstein, Kris Cao, He He, Felix Hill, Spandana Gella, Jamie Kiros, Hongyuan Mei and Dipendra Misra, and advised by Kyunghyun Cho, Edward Grefenstette, Karl Moritz Hermann and Laura Rimell. The 3rd Workshop on Representation Learning for NLP aims to continue the success of the 1st Workshop on Representation Learning for NLP, which received about 50 submissions and over 250 attendees and was the second most attended collocated event at ACL 2016 in Berlin, Germany after WMT; and the 2nd Workshop on Representation Learning for NLP at ACL 2017 in Vancouver, Canada. The workshop has a focus on vector space models of meaning, compositionality, and the application of deep neural networks and spectral methods to NLP. It provides a forum for discussing recent advances on these topics, as well as future research directions in linguistically motivated vector-based models in NLP.