While scanning probe microscopy (SPM) is extensively used to obtain topographical images at the nano-scale, efforts to achieve chemical characterization with comparable lateral resolution are still under development. Apertureless near-field Raman spectroscopy, a combination of SPM and Raman spectroscopy, is a promising technique for nano-scale chemical imaging. It is based on enhancement of the Raman signal in the vicinity of a metal or metallized probe of the SPM (the so-called tip-enhanced Raman spectroscopy, TERS). We overview TERS results accumulated by various groups. TERS has been applied to analysis of different materials, including organic dyes, biological molecules, single walled carbon nanotubes and silicon, and achieved unprecedented for optical spectroscopy resolution ~10-20 nm. Reproducible enhancement of the Raman signal of the order of 10³ – 10⁴ has been achieved in various groups. This enhancement, however, is not sufficient for high contrast of the near-field to far-field signals. The latter appears as a background in apertureless near-field optical spectroscopy and currently presents the main obstacle in its broad applications. On the example of silicon, we emphasize that, by optimizing the polarization geometry, high contrast between the near-field and far-field signals can be achieved. That makes the technique attractive for various applications. Future of the near-field optical spectroscopy and the main challenges are discussed at the end.