This document discusses distributed deep learning on Hadoop clusters using CaffeOnSpark. CaffeOnSpark is an open source project that allows deep learning models defined in Caffe to be trained and run on large datasets distributed across a Spark cluster. It provides a scalable architecture that can reduce training time by up to 19x compared to single node training. CaffeOnSpark provides APIs in Scala and Python and can be easily deployed on both public and private clouds. It has been used in production at Yahoo since 2015 to power applications like Flickr and Yahoo Weather.