Silicon nanoparticles (SiNPs) are regarded as a promising alternative of traditional II-VI quantum dots in the field of bio-applications due to their photoluminescence and bio-compatibility. Chapter 1 reviews various synthetic routes and applications of SiNPs. Chapter 2 describes the mechanochemical synthesis of photoluminescent SiNPs with an organic ligand shell through reactive high energy ball milling (RHEBM). The morphology and size distribution of as-prepared SiNPs were determined by TEM. The bonding modes of the ligand shell including their mole fractions were investigated based on NMR and FTIR spectra of the as-prepared SiNPs.Chapter 3 introduces the removal of the iron impurities, which were introduced into the SiNPs product from the milling media, stainless steel, by a physical method (GPC) and a chemical method (washing by HCl aqueous solution). The effect of the iron impurities to the optical properties of SiNPs is discussed.Chapter 4 exhibits the surface functionalization of SiNPs with various functional groups through thiol-ene click reactions of vinyl-terminated SiNPs with various thiols. In addition, SiNP nanoclusters and DNA-conjugated SiNPs were prepared through thiol-ene click reactions of vinyl-terminated SiNPs with a tetrathiol-terminated crosslinker and a thiol-functionalized DNA, respectivelyChapter 5 is a miscellaneous chapter which includes the preparation of SiNPs through RHEBM of silicon wafers with 2,3-dimethyl-1,3-butadiene, and the effect of UV irradiation at 254 nm to the chemical structures and optical properties of SiNPs.