Relevant fundamentals of the electrochemical double layer and supercapacitors utilizing the interfacial capacitance as well as superficial redox processes at the electrode/solution interface are briefly reviewed. Experimental methods for the determination of the capacity of electrochemical double layers, of charge storage electrode materials for supercapacitors, and of supercapacitors are discussed and compared. Intrinsic limitations and pitfalls are indicated; popular errors, misconceptions, and mistakes are evaluated. The suitability of available methods is discussed, and practical recommendations are provided.