When inserted into certain phospholipid membranes in sufficient amounts, cholesterol (CHOL) induces the liquid ordered (L o ) phase, whose properties are intermediate between the liquid disordered (L d ) and gel phases: acyl chains display gel-like ordering, whereas rotational and translational diffusion is relatively fast akin to the L d phase. CHOL increases order, thickness, and stiffness of the L d phase, yet has the opposite effects on the gel phase. Therefore, binary mixtures of CHOL and certain phospholipids have a threshold CHOL concentration, above which the L d -gel transition vanishes. For dipalmitoylphosphatidylcholine (DPPC) this happens at ≈25-30 mol% of CHOL, above which the membrane properties show continuous temperature dependence, indicating a uniform L o phase. This behavior is reported by numerous experimental approaches and simulations. Still, some studies have reported nonidealities within the L o region: differential scanning calorimetry (DSC) and NMR detected a broad transition, which was suggested to correspond to the transition between two distinct L o phases differing in lipid chain tilt. NMR spectroscopy and X-ray scattering suggested that even at high CHOL concentrations, heating melts the glycerol region, shifts CHOL towards lipid headgroups, and disorders acyl chain termini. Certain ternary mixtures of low-T m and high-T m lipids and CHOL display L o /L d coexistence, modelling the putative lipid domains ("rafts") in biomembranes. The coexistence is visible at temperatures below the T m of the high-T m lipid, and similarly in giant plasma membrane-derived vesicles well below the body temperature. This agrees with CHOL's ability to melt the gel phase, and recent simulations have indeed demonstrated ordered phases with hexagonally-packed and CHOL-depleted regions, 21-23 despite CHOL's preference for saturated chains. However, it is unclear whether the L o phase observed in phase-separated vesicles structurally differs from that observed at higher T , and whether the former is a faithful model plasma cell membrane heterogeneity.