POLENET/LAPNET broadband seismic network was deployed in northern Fennoscandia 2007–2009. In our study we estimate the 3D architecture of the upper mantle beneath the network using high-resolution teleseismic P-wave tomography. Our study reveals a highly heterogeneous lithospheric mantle. The most significant feature seen in the obtained velocity model is a large elongated low-velocity anomaly beneath the crust, separating the three cratonic units that formed the region in the early Proterozoic.