Every day we come across different types of changes. Turning day into night, night into a day, rising and setting of sun and moon, changing of climate, melting of ice, and lot more. These changes occur in a minute or may take a longer time. Few changes are not even noticeable. This chapter sheds light on reversible and irreversible changes around us, Expansion and Contraction, Anomalous expansion of water, along with the difference that may occur by heating a substance or by mixing it with some other.