Reaction models are proposed to quantify the hydration products and to determine the composition of C-S-H from alkali-activated slags (AAS). Products of the slag hydration are first summarized from observations in literature. The main hydration products include C-S-H, hydrotalcite, hydrogarnet, AFm phases (C(4)AH(13) and C(2)ASH(8)) and ettringite. Then, three stoichiometric reaction models are established correlating the mineral composition of slag (the glass part) with the hydration products. Using the proposed models, quantities of hydration products and composition of C-S-H are determined. The models are validated with a number of experimental investigations reported in literature, yielding good agreement, i.e., these models can successfully predict the hydration reaction of AAS. The models are furthermore applied to calculate the retained water in the hydration products of AAS in different hydration states and a general hydration equation of AAS is derived. As an illustration to one of the model applications, chemical shrinkage of the AAS cement paste in different hydration states are predicted. The chemical shrinkage of AAS is shown to be remarkably higher than OPC. Furthermore, phase distribution in the hardened AAS paste and the porosity are calculated.