Materials which are both ferromagnetic and ferroelectric like yttrium manganite have interesting features and applications as non-volatile memory devices. In this book different properties of Yttrium Manganite is investigated using first principle calculation on cubic and Hexagonal structures. Electronic structures, phonon modes and structural stabilities are one of the properties that has been discussed. DFT calculations of such strongly correlated materials shows metallic ground state though they are insulators. In order to correct this we implement Generalized Gradiednt Approximation (GGA) plus Hubbard U correction to density functional theory found interesting results. All the results in this book were done using electronic structure simulation code, Quantum Espresso (QE).