Emission line B-type stars. Fundamental parameters, stellar winds and circumstellar environments
B-type stars encompass distinct stellar groups with established evolutionary status: pre-main sequence (PMS) stars, main sequence stars, blue supergiants, and post-AGB stars. In particular evolutionary stages, even during the main sequence stage, some B-type stars exhibit intense spectral emission lines, mainly the H$\alpha$ and single ionised metals. Other stars show, in addition, forbidden emission lines, large IR excess due to the presence of a dusty ring-like structure and, sometimes, molecular emission. Most of these stars are deeply embedded in their circumstellar media, making it extremely difficult to assign fundamental parameters or spectral types. I describe some photometric and spectroscopic criteria that often help to improve the classification of peculiar B-type stars. I also include a brief description of our theoretical work on stellar winds.