Diabetes mellitus is one of the common metabolic diseases which severely affect many organs in the body. It involves perturbation of carbohydrate, fat and protein metabolisms and affects a great amount of the world's population. In this chapter, the application of vibrational spectroscopy, namely Infrared and Raman spectroscopy together with microspectroscopy, and Terahertz spectroscopy to the screening and diagnosis of diabetes will be discussed. In the first section, molecular mechanism and the pathophysiology of diabetes are summarized. In the following parts, brief information about the non-invasive blood glucose measurement techniques are mentioned, and the applications of vibrational spectroscopy to the diagnosis of diabetes are given. Vibrational spectroscopic applications are generally used together with different statistical analysis methods and chemometric tools, such as cluster analysis and artificial neural networks which provide determination of diabetes induced changes in various tissue macromolecules. Based on these variations, the discrimination of diseased state from the healthy subjects will become possible. Spectroscopic techniques have growing applicability due to their advantages over conventional techniques. They allow the visualization of the presence and state of the diseases depending on specific spectral database. By this way, the early diagnosis of metabolic diseases, such as diabetes will be possible by analyzing the variations in spectral parameters. Thus, understanding the basis of these spectroscopic techniques become an important issue in terms of the disease recognition.