In cyanobacteria, major halotolerant mechanisms, such as ion homeostasis and the biosynthesis of osmoprotectant molecules, are activated under salt stress conditions. In addition to these salt stress-specific pathways, basic metabolic processes such as carbon and nitrogen metabolism, P metabolism, and lipid metabolism can also respond to salt stress, as described in the previous chapters. In this chapter, we discuss other physiological phenomena that are collectively regulated in response to salt stress in cyanobacteria, such as protein homeostasis, redox regulation, the 1C metabolic pathway, and circadian rhythms. We will proceed with the discussion by referring to the results of biochemical analyses of the factors involved in each process and the results of proteomic analyses conducted using halotolerant cyanobacteria.