Title: Slot Machines: Discovering Winning Combinations of Random Weights in Neural Networks. Abstract: In contrast to traditional weight optimization in a continuous space, we demonstrate the existence of effective random networks whose weights are never updated. By selecting a weight among a fixed set of random values for each individual connection, our method uncovers combinations of random weights that match the performance of trained networks of the same capacity. We refer to our networks as ``slot machines'' where each reel (connection) contains a fixed set of symbols (random values). Our backpropagation algorithm ``spins'' the reels to seek ``winning''  combinations, i.e., selections of random weight values that minimize the given loss. Quite surprisingly, we find that allocating just a few random values to each connection (e.g., 8 values per connection) yields highly competitive combinations despite being dramatically more constrained compared to traditionally learned weights. Moreover, finetuning these combinations often improves performance over the trained baselines.  A randomly initialized VGG-19 with 8 values per connection contains a combination that achieves 90% test accuracy on CIFAR-10.  Our method also achieves an impressive performance of 98.1% on MNIST for neural networks containing only random weights. 