For many protein purifications a sequence of different methods is used to achieve pure protein. The protein purification strategy describes the combination of several method steps and divides them into capture, intermediate and polishing step. The “capture” step purifies the protein from the crude extract. The “intermediate” step removes further contamination, while the aim of the final “polishing” step is to get rid of all remaining impurities to gain a highly purified product. Depending on the yield and purity of the protein which is needed for further analysis and /or use of the protein, several steps are combined. In most cases two or (slightly rarer) three steps for protein purification are combined. Nevertheless, purification strategies with just one step or more than three steps are possible as well.