Coding schemes for the binary memoryless T-user adder channel are investigated in this paper. First upper and lower bounds on the capacity sum, which are asymptotically tight with increasing T, are derived for the noiseless case. Second, a class of T-user uniquely decodable codes with rates, asymptotically in T, equal to the maximal achievable values is constructed. A decoding algorithm for these codes is also presented. Next, a class of error-correcting codes for the noisy T-user adder channel is constructed. It is shown that these codes can be used to construct multi-level codes suitable for use on the additive white Gaussian noise channel. ©1979 IEEE