Multiuser multiple-input multiple-output (MIMO) is a crucial technique to increase the channel capacity and improve communication qualities in the fifth-generation (5G) wireless communication systems. This chapter considers the code design for multiuser MIMO system. It proposes an interleave-division multiple-access (IDMA)-based multiuser repetition-aided irregular repeat accumulate (IRA) code for this system. Both of the low density parity check (LDPC)-like and turbo-like decoding schemes are accomplished by iterative processing between a multiuser detection (MUD) and multiple single-user decodings. The decoding error performance can be predicted by the EXIT functions. The chapter provides numerical results for the code optimizations for multiuser systems over both AWGN and Rayleigh fading channels. It compares the performances of two decoding schemes of LDPC-like and turbo-like decodings and shows that the optimal codes for LDPC-like decoding also perform well under turbo-like decoding, which converges even faster due to a posterior probability processing for the accumulation.