Nanotechnology is defined as the understanding, manipulating and controlling things at the nanoscale, where the unique properties of materials arises that enable novel applications. Gold is considered to be noble among all metals due to its resistance to surface oxidation because of this, it is known as the king of the metals. Contrary to the nobility of bulk gold, exciting properties can be attributed to gold at the nanoscale. Gold nanoparticles (AuNps) can be used for clinical developments in cell labeling, providing contrast in biological imaging, drug design and time bound delivery at the specific location of the disease. This book contains the techniques of preparing different sizes of gold nanoparticles stabilized with citrate, starch and gum arabic. The AuNps were studied for their in vitro stability as a function of time of storage at room temperature, change of pH and the addition of different concentration of an electrolyte. In vitro cytotoxicitiy studies were performedon gold nanoparticles with different sizes and different stabilizer. MTT, LDH and Neutral red cell cytotoxicity assay were performed on gold nanoparticles with MCF-7 and PC-3 cell lines. The AuNps