Average and substorm conditions in the lobe and plasma sheet regions of the earth's magnetotail are studied as a function of downstream distance and east‐west location using ISEE 3 magnetometer and plasma analyzer measurements. On the basis of 756 magnetopause crossings a low‐latitude magnetotail diameter of 60±5 R_E at |X| = 130 ‐ 225 R_E is determined. The strength of the lobe magnetic field from |X| = 20 to 130 R_E is shown to fall off as X^{−0.53±0.05}. Flaring ceases on average at |X| = 120 ± 10 R_E with a relatively constant B_L = 9.2 nT beyond that distance. The ratios |B_y/B_x| and |B_z/B_x| in the translunar tail lobes are small and relatively constant with mean values of 0.10 and 0.06, respectively. These results are shown to be in good agreement with the Coroniti‐Kennel flaring tail models of lobe magnetic field configuration with slightly enhanced B_y due to Maxwell stresses exerted at the magnetopause by the solar wind. The plasma parameters V_x, n_e, β_e, and M_A in the lobes all increase with distance down the tail while T_e decreases. The mean values of these lobe quantities at |X| = 200 ‐ 220 R_E are V_x = −200 ‐ 250 km/s, n = 0.1 ‐ 0.2 cm⁻³, β_e = 0.02 ‐ 0.05, M_A = 0.3 ‐ 0.4, and T_e = 5 ‐ 8×10⁵ °K. Strong density and weak velocity and temperature gradients are observed as ISEE 3 moves from the center of the lobes out toward the magnetopause. In particular, factor of 3–6 increases in plasma density are observed as the spacecraft moves from the center of the tail at |Y′| < 10 R_E (Y′ refers to the aberrated GSM system) toward the dawn and dusk portions of lobes at |Y′| > 20 R_E. Good agreement is found between the leaky magnetopause model of Pilipp and Morfill (1978) and the strong density/weak velocity gradients observed in the lobes. Substorm activity, as measured by AE(9), is only weakly correlated with magnetic field strength, electron beta, or Alfvénic Mach number in the lobes at |X| > 200 R_E. The plasma sheet magnetic field intensity and electron temperature decrease with increasing downstream distance, while flow speed, density, and Alfvénic Mach number all increase. Average plasma sheet parameters at |X| = 200 ‐ 220 R_E are B = 4.0 nT, V_x = −500 km/s, n_e = 0.3 cm⁻³, T_e = 1.2×10⁶ °K, and M_A = 2.7. Electron beta is independent of downstream distance with a mean value of approximately 0.7. On the basis of pressure balance arguments the estimated total plasma beta in the |X| > 60 R_E plasma sheet is 4.5, and the T_i/T_e ratio is 5.5. With respect to reconnection, the most significant results are the correlations between B_z, V_x, and AE(9) in the plasma sheet, the variation in these parameters with X and ± Y, and their implications for the location of the distant neutral line. The highest tailward flow speeds are found to be proportional to the magnitude of the embedded southward B_z. Furthermore, both tailward V_x and southward B_z are shown to be well correlated with AE(9). Earthward of |X| = 100 R_E the average B_z is northward and the flow is on average sub‐Alfvénic. Between |X| = 100 and 180 R_E the flow becomes predominantly tailward and super‐Alfvénic, M_A = 1 ‐ 2, across the entire width of the tail. However, the average magnetic field is found to be southward only in a 10 R_E wide region near the aberrated noon‐midnight meridian. At |X| = 180 ‐ 225 R_E the flow speed is somewhat higher, M_A = 2 ‐ 3, and the width of the region of southward B_z grows to 30 R_E. Tailward flow speed and electron temperature exhibit maxima in the central portion of the plasma sheet where B_z < 0. However, at |Y′| > 15 R_E, where B_z > 0, the flow direction remains tailward, albeit at a reduced speed. The magnetic field results are interpreted in …