[en] Due to recent availability and analyses of high time resolution satellite data (including IMP 6 and the ISEE-1 and -2 satellite pair), the study of the magnetopause and boundary layer has entered a period of renewed activity. Plasma observations from the VELA satellites first established the presence of magnetosheath-like plasma with reduced density and flow velocity in a relatively thin (approx.<1 R/sub E/) layer bordering the plasma sheet at low latitudes and bordering the lobe environment at high latitudes. Recent analyses of HEOS 2, Explorer 33 and IMP 6 data have established the presence of this ''plasma boundary layer'' (PBL) over the entire sunward magnetosphere near the magnetopause. This review gives a brief summary of recent published results on two distinct regions of the PBL: that bordering open field line regions and that bordering closed field line regions. The magnetopause layer (i.e., current layer) can usually be identified by a change in magnetic field direction and cannot be uniquely identified by any other field or plasma parameters. Immediately earthward of this magnetopause current layer, a PBL of magnetosheath-like plasma is usually observed that has dominantly magnetosheath-like energy spectra and flow characteristics. Observed plasma boundary layer thicknesses are highly variable and are generally much larger than the magnetopause layer thicknesses even near the subsolar region. Several suggested source mechanisms for the plasma boundary layer are discussed and compared