To reduce the impact of fading and maintain desire quality-of-service (QoS) amidst the increasing network data traffic, it is essential to focus on diversity schemes. This chapter introduces the different types of diversity combining techniques such as space diversity, frequency diversity, time diversity, and polarization diversity. Specifically, this chapter focuses on the analysis of space diversity schemes with respect to indoor optical wireless networks. In addition, a detailed analysis of the capacity in optical wireless multiuser systems in the presence of discrete-time Poisson channels, optical intensity channels with input-dependent Gaussian noise, and free-space optical intensity channels are also presented in this chapter.