Without secure commercial information exchange and safe electronic financial transactions over mobile networks, neither service providers nor potential customers will trust mobile commerce. Various mobile security procedures and payment methods have been proposed and applied to mobile commerce, and this chapter attempts to provide a comprehensive overview of them. A secure mobile commerce system must have the following properties: (i) confidentiality, (ii) authentication, (iii) integrity, (iv) authorization, (v) availability, and (vi) non-repudiation. This chapter discusses the security issues related to the following three network paradigms: (i) wireless local area networks, (ii) wireless wide area networks, and (iii) WAP. Among the many themes of mobile commerce security, mobile payment methods are probably the most important. A typical mobile payment process includes: (i) registration, (ii) payment submission, (iii) authentication and authorization by a content provider, and (iv) confirmation. This chapter also describes a set of standards for mobile payments.