|Abstract:||A measurement of the polarization of the W boson from top quark decay is an excellent test of the V-A form of the charged-current weak interaction in the standard model. Since the longitudinal W boson is intimately related to the electroweak symmetry breaking mechanism, and the standard model gives a specific prediction for the fraction longitudinal W bosons from top decays, it is of particular interest for study. This thesis presents a measurement of W boson polarization in top quark decays through an analysis of the co9 distribution in the lepton-plus-jets channel of the tt candidate events from pp collisions at (see document for equation). This measurement uses an integrated luminosity of (see document) of data collection with the CDF Run II detector, resulting in 31 tt candidate events with at least one identified 5 jet. Using a binned likelihood fit to the co9 distribution from the tt candidate events found in this sample, the fraction of W bosons with longitudinal polarization is determined to be (equation. This result is consistent with the standard model prediction, gives a top quark mass of 174.3 GeV/e2, of (see document).