In market economies, sustainability goals can be achieved if sustainable behaviour creates benefits for corporations. Market partners may have preferences for sustainability so that their decisions to buy products, make investments or choose workplaces depend on the good behaviour of corporations, namely on their social, ethical and ecological track record. However, it is difficult for stakeholders to measure sustainable corporate behaviour. Certification schemes can help to overcome this information asymmetry. If designed properly they provide a means for sustainable companies to signal their good behaviour to the market. Such signals make it easier for market actors to differentiate when making their respective market choices. While certificates for products are widespread and thoroughly researched, certificates for good companies have not yet drawn much academic attention, even though various certification schemes have evolved in different jurisdictions. This chapter compares these different certification schemes and analyses them from a regulatory perspective.