Earth's magnetosphere is electromagnetically coupled to its ionosphere by field-aligned currents (FACs) comprising two large-scale elements, Region 1 (R1) and Region 2 (R2) currents, which were discovered by Potemra (1976a, 1976b) in the ionosphere (Figure 1a). Region 1 currents, which are at higher latitudes, consist of FACs flowing downward into the ionosphere in the dawn sector and upward out of the ionosphere in the dusk sector. Equatorward of R1 currents lie R2 currents, which flow in the opposite directions. Regions 1 and 2 currents largely overlap the auroral oval, the ionospheric footprint of the plasma sheet. In the magnetosphere (Figure 1b), R1 current occupies a large volume, including the magnetopause, the plasma sheet boundary layer, and the outer (high invariant latitude) plasma sheet. Region 2 current occupies the inner (lower invariant latitude) plasma sheet, including the central plasma sheet, and part of the inner magnetosphere (e.g., Cowley, 2000;Ohtani et al., 1988Ohtani et al., , 2010Tanaka, 1995). The equatorial footprint of the interface between R1 and R2 currents is at ∼8-12 R E downtail on the nightside (Liu et al., 2016). These currents, which arise from large-scale M-I convection and its resultant magnetic field distortions and pressure gradients (Tanaka, 1995), are critical to imposing magnetic stress, modifying plasma flow, and transmitting energy between the ionosphere and the magnetosphere (e.g., Vasyliunas, 1970).Well-approximated as current sheets elongated in the east-west direction (Figure 1; in this paper, east, west, north, and south refer to magnetic east, west, north, and south, respectively), R1 and R2 currents cause deflection of the east-west magnetic field (B E ) in the ionosphere. Potemra (1976a, 1976b) relied on the B E deflection profile as a function of magnetic latitude to discover R1 and R2 currents, and it remains a Abstract Regions 1 and 2 (R1 and R2) field-aligned currents (FACs), manifestations of large-scale convection in Earth's magnetosphere-ionosphere (M-I) system, often contain intense FAC layers of mesoscale latitudinal width near the R1/R2 interface. We refer to such layers as "embedded" R1 and R2 FACs. Likely resulting from enhanced magnetosphere-ionosphere (M-I) convection, these FACs may indicate M-I configuration change and contribute significantly to substorm current wedges. We present several events in which embedded FACs were observed by low-altitude spacecraft in the ionosphere. All the events occurred during active geomagnetic conditions or a substorm growth phase, and most map to an equatorial location on the nightside. When an embedded FAC is upward, it coincides with inverted-V electron precipitation and a discrete auroral arc. If an upward embedded FAC is in the postmidnightto-dawn sector, a dawnside auroral polarization stream appears immediately poleward of it, so it may be important for ionospheric heating, M-I convection, and instabilities. Our results establish embedded FACs as a frequently appearing, fundamental phenomenon for under...