Hydrodynamics characterization in terms of flow regime behavior is a crucial task to enhance the design of bubble column reactors and scaling up related methodologies. This review presents recent studies on the typical flow regimes established in bubble columns. Some effort is also provided to introduce relevant definitions pertaining to this field, namely, that of "void fraction" and related (local, chordal, cross-sectional and volumetric) variants. Experimental studies involving different parameters that affect design and operating conditions are also discussed in detail. In the second part of the review, the attention is shifted to cases with internals of various types (perforated plates, baffles, vibrating helical springs, mixers, and heat exchanger tubes) immersed in the bubble columns. It is shown that the presence of these elements has a limited influence on the global column hydrodynamics. However, they can make the homogeneous flow regime more stable in terms of transition gas velocity and transition holdup value. The last section is used to highlight gaps which have not been filled yet and future directions of investigation.