We report a summary of the symposium "Stress and Protists: No life without stress", which was held in September 2015 on the VII European Congress of Protistology in partnership with the International Society of Protistologists (Seville, Spain). We present an overview on general comments and concepts on cellular stress which can be also applied to any protist. Generally, various environmental stressors may induce similar cell responses in very different protists. Two main topics are reported in this manuscript: (i) metallic nanoparticles as environmental pollutants and stressors for aquatic protists, and (ii) ultraviolet radiation - induced stress and photoprotective strategies in ciliates. Model protists such as Chlamydomonas reinhardtii and Tetrahymena thermophila were used to assess stress caused by nanoparticles while stress caused by ultraviolet radiation was tested with free living planktonic ciliates as well as with the symbiont-bearing model ciliate Paramecium bursaria. For future studies, we suggest more intensive analyses on protist stress responses to specific environmental abiotic and/or biotic stressors at molecular and genetic levels up to ecological consequences and food web dynamics.