Lipids are the major substance in biological membrane. They also make an important role for industrial applications such as food, pharmaceutical and cosmetics. Here, we have reviewed the physical chemistry of lipids, especially, highlighted to triacylglycerols (TAGs) and phospholipids. In the TAGs part, the thermal and structural properties of PPP and POP, the typical TAGs, have been focused on. The complicated polymorphism is present in TAGs. In order to determine polymorphs, time-resolved synchrotron radiation X-ray diffraction measurement and differential scanning calorimetry (DSC) under the same conditions, simultaneous or even though not simultaneous, is effective. As for phospholipid part, at first, the type of phospholipid and relationship between phospholipid and bio-membrane has been introduced. Secondly, crystal structure of phospholipid has also been introduced. Thirdly, the polymorphism and phase transitions of phospholipids under excess water, namely hydrated membrane state, have been highlighted. DSC data and its analysis, transition temperature, transition enthalpy and conformation entropy, have been explained and discussed. Finally, an interesting topic about the relationship between phase transition and life activity has been introduced.