One of the greatest challenges in cancer drug therapy is to maximize the effectiveness of the active agent while reducing its systemic adverse effects. To add more, many widely-used chemoterapeutic agents present unfavorable physicochemical properties (e.g. low solubility, lack of chemical or biological stability) that hamper or limit their therapeutic applications. All these issues may be overcome by designing adequate drug delivery systems; nanocarriers are particularly suitable for this purpose. Nanosystems can be used for targeted-drug release, treatment, diagnostic imaging and therapy monitoring. They allow the formulation of drug delivery systems with user-defined characteristics regarding solubility, biodegradability, particle size, release kinetics and active targeting, among others. This review (Part I) focuses on recent patents published between 2008 and the present day, related to nanospheres, nanocapsules and nanogels applied to anticancer drug therapy. Other nanosystems is covered in a second article (Part II).