Some microgels, soluble in water, change their solubility state with temperature. PNIPAM microgels dispersed in water, for example, expel water and become smaller if the temperature of the dispersion exceeds 32°C. This temperature-sensitive behavior is fully reversible and can be theoretically calculated. PNIPAM particles also show co-nonsolvency. This means PNIPAM particles are soluble in water and, e.g., methanol at room temperature, but not in certain mixtures of both. The work by Walter Richtering et al. on page 1100 of this joint special issue between the Journal of Polymer Science, Part A: Polymer Chemistry and Part B: Polymer Physics addresses the temperature-sensitive behavior of PNIPAM microgels in co-nonsolvent mixtures of methanol and water and the theoretical description of this behavior.