Detailed growth mechanism of nanoparticles with formula and physics associated with it is explained. Most of synthesis techniques used to prepare nanoparticles is discussed in detail. Basic interaction as well as interpretation between nanoparticles and electromagnetic radiation is discussed in terms of direct and indirect energy band gap. Further, how a basic optical property changes when materials dimensions are reduces to nanometer is also explained with the help of quantum mechanics. Energy band gap for semiconducting single crystal is explained in term of mathematics and main concepts of physics behind that mathematics. Quantum confinement effect had discussed in terms of energy band gap of nanoparticles and also how energy band gap controls particle size. How and why size of nanoparticles plays a important role in altering the properties of material is also discussed in depth. Mathematically Urbach rule as well as Effective Mass Approximation is presented in this book. Effect of doping in all properties like electrical, magnetic, dielectric, optical, thermal, structural as well as synthesis temperature and many more properties changes, it is briefly discussed.