**1. Introduction**

The main purpose of this chapter is to present an alternative to the Standard Model (SM) (Gottfried and Weisskopf, 1984) of particle physics. This alternative model, called the Generation Model (GM) (Robson, 2002; 2004; Evans and Robson, 2006), describes all the transition probabilities for interactions involving the six leptons and the six quarks, which form the elementary particles of the SM in terms of only three unified additive quantum numbers instead of the nine non-unified additive quantum numbers allotted to the leptons and quarks in the SM.

The chapter presents (Section 2) an outline of the current formulation of the SM: the elementary particles and the fundamental interactions of the SM, and the basic problem inherent in the SM. This is followed by (Section 3) a summary of the GM, highlighting the essential differences between the GM and the SM. Section 3 also introduces a more recent development of a composite GM in which both leptons and quarks have a substructure. This enhanced GM has been named the Composite Generation Model (CGM) (Robson, 2005; 2011a). In this chapter, for convenience, we shall refer to this enhanced GM as the CGM, whenever the substructure of leptons and quarks is important for the discussion. Section 4 focuses on several important consequences of the different paradigms provided by the GM. In particular: the origin of mass, the mass hierarchy of the leptons and quarks, the origin of gravity and the origin of apparent CP violation, are discussed. Finally, Section 5 provides a summary and discusses future prospects.
