Mixed-matrix membranes, MMM, have been a very popular research topic for many scientists in many fields during the last few years. This work provides an overview of general properties, interesting structural components, potential applications, as well as pitfalls and drawbacks in the preparation of membranes of this type. MMM, especially when combined with ionic liquids, IL, and/or organometallic frames, MOF, represent one of the best and very promising options for industrial applications, specifically for the capturing and separation of CO2. As a result, the properties of these two fillers (IL and/or MOF) can enable us to prepare membranes with a higher separation and permeability efficiency, chemical and mechanical resistance, and thermal stability. Unfortunately, the toxicity and stability of the individual components of the membranes and the resulting mixed matrix membranes have not yet been investigated in detail and further research is needed. One of the main drawbacks is a very high cost of the production of the individual parts and the subsequent assembly of these composite membranes. This is the reason why we still do not see these MMM being used widely in industry.