We present a review of the inflationary scenario. A description of the Cosmological Standard Big Bang Model (CSM) is given and it is explained how the problmes of the CSM are solved by infalction, i.e., the horizon, flatness, large scale structures and monopole problems. In particualr, it is shown that inflation with a duration of 60 Hubble times impleis an increase in the horizon distance dH by 27 orders of magnitude, a decrease in the denisity parameter minus 1 by 54 orders of magnitude and a dilution of the concentration of monopoles by 78 orders of magnitude. Moreove, the Slow Roll approximation (SR), whihc is a specific model of inflation, is described. The parameters of this model can be directly compared with cosmological observations. Using the results from the Wilkinson Microwave Anisotropy Probe three-year data (WMAP3), it shall be argued that the SR approximateion is a valid model for the early Universe.