A measurement of the average b hadron lifetime is reported. Electrons from hadronic events produced at the PEP $ e^{+}e^{-} $ storage ring are studied. The impact parameters of these electrons are used to determine the lifetime of hadrons containing bottom quarks. The result is $ 1.16_{-0.34}^{+0.37}(stat)\pm0.23(sys) $ psec. This result constrains elements of the Kobayashi-Maskawa mixing matrix. The analysis uses the impact parameter method, which relies on prompt electrons from semileptonic decays of charm and bottom hadrons. The measurement uses a Čerenkov identified sample of prompt electrons with momenta as low as 1 GeV/c, reducing background contamination. The lifetime is derived from the impact parameter, which is the distance of closest approach of the electron to the center of the $ e^{+}e^{-} $ beams projected onto a plane perpendicular to the beams. The thrust axis of the event is used to approximate the parent hadron direction, and the sign of the impact parameter is given by the sign of the apparent decay length. The impact parameter distributions for electrons in the b and c regions are shown in Figs. 2(a) and 2(b). The means of these distributions are $ \bar{\delta} = 215 \pm 81 \, \mu m $ for the b region and $ \bar{\delta} = 137 \pm 54 \, \mu m $ for the c region. These values are larger than previous measurements. Experimental cross checks using three different data sets confirm the results. A maximum likelihood fit using all tracks with $ |\delta| < 3 $ mm is performed to extract the b quark lifetime from the electron data set. The most likely values of $ \tau_{b} $ and $ \tau_{c} $ are $ 1.33_{-0.36}^{+0.39} $ psec and $ 0.77_{-0.42}^{+0.50} $ psec, respectively. These values are consistent with previous measurements. The average lifetime of hadrons containing b quarks is measured to be $ \tau_{b}=1.16_{-0.34}^{+0.37}(stat)\pm0.23(sys) $ psec. This result is used to constrain the matrix elements $ |V_{bu}| $ and $ |V_{bc}| $, which describe the transitions between the b quark and the u and c quarks. The measured value of $ \tau_{b} $ is consistent with previous measurements. The systematic error on $ \tau_{b} $ is 20%.A measurement of the average b hadron lifetime is reported. Electrons from hadronic events produced at the PEP $ e^{+}e^{-} $ storage ring are studied. The impact parameters of these electrons are used to determine the lifetime of hadrons containing bottom quarks. The result is $ 1.16_{-0.34}^{+0.37}(stat)\pm0.23(sys) $ psec. This result constrains elements of the Kobayashi-Maskawa mixing matrix. The analysis uses the impact parameter method, which relies on prompt electrons from semileptonic decays of charm and bottom hadrons. The measurement uses a Čerenkov identified sample of prompt electrons with momenta as low as 1 GeV/c, reducing background contamination. The lifetime is derived from the impact parameter, which is the distance of closest approach of the electron to the center of the $ e^{+}e^{-} $ beams projected onto a plane perpendicular to the beams. The thrust axis of the event is used to approximate the parent hadron direction, and the sign of the impact parameter is given by the sign of the apparent decay length. The impact parameter distributions for electrons in the b and c regions are shown in Figs. 2(a) and 2(b). The means of these distributions are $ \bar{\delta} = 215 \pm 81 \, \mu m $ for the b region and $ \bar{\delta} = 137 \pm 54 \, \mu m $ for the c region. These values are larger than previous measurements. Experimental cross checks using three different data sets confirm the results. A maximum likelihood fit using all tracks with $ |\delta| < 3 $ mm is performed to extract the b quark lifetime from the electron data set. The most likely values of $ \tau_{b} $ and $ \tau_{c} $ are $ 1.33_{-0.36}^{+0.39} $ psec and $ 0.77_{-0.42}^{+0.50} $ psec, respectively. These values are consistent with previous measurements. The average lifetime of hadrons containing b quarks is measured to be $ \tau_{b}=1.16_{-0.34}^{+0.37}(stat)\pm0.23(sys) $ psec. This result is used to constrain the matrix elements $ |V_{bu}| $ and $ |V_{bc}| $, which describe the transitions between the b quark and the u and c quarks. The measured value of $ \tau_{b} $ is consistent with previous measurements. The systematic error on $ \tau_{b} $ is 20%.