Climate change and marine pollution are highlighted as research priority areas in the algal biology. These two issues are likely key drivers in the functioning of ecosystems and maintenance of biodiversity that affects individual species and have a significant impact on marine coastal ecosystems. Marine macroalgae commonly known as seaweeds are the assemblage of diverse group of sessile plants predominantly occur in coastal waters. This monograph described the various adaptive strategies and tolerance mechanisms of seaweeds to withstand diverse and adverse environmental stress conditions in their ecological niche. Specifically, the results of this research can be used to assess how resilient seaweeds are to environmental change. The undertaken study in this monograph is highly significant and has addressed key questions of globally recognized relevance and importance to enhance our understanding on the mechanisms underlying responses of marine algae to changing climate and contaminants. This monograph will enhance the reputation and attractiveness of algae for researchers working in diverse fields such as aquatic pollution, climate change, stress biology and ecotoxicology.