The article reviews the mechanisms underlying the development and evolution of thalamocortical connectivity in mammals. Thalamocortical axons (TCAs) navigate through the forebrain, crossing boundaries such as the pallial-subpallial boundary (PSPB) and the diencephalic-telencephalic boundary (DTB). The PSPB, in particular, presents a significant challenge for TCAs, with various guidance defects observed in mutant mice. Early thalamocortical projections from subplate neurons and corticofugal axons from the lateral ganglionic eminence (LGE) assist TCAs in crossing these boundaries. The "handshake hypothesis" suggests that these interactions help TCAs navigate through the PSPB. Genetic studies, such as those involving *Emx2* and *Arid1a*, have revealed the importance of transcription factors and subplate neurons in guiding TCAs. TCAs accumulate in the subplate zone during a "waiting" period before invading the cortical plate, where they form transient synapses with subplate neurons. The evolution of the PSPB has significantly impacted thalamocortical connectivity, with changes in genes like *Pax6* contributing to these differences. Thalamocortical activity is crucial for cortical development, influencing the formation of barrels, cytoarchitectonic patterns, and interneuron morphologies. Thalamic regulation also affects cortical neurogenesis and laminar development. The precise targeting of TCAs to specific cortical areas is established through interactions with subplate neurons and L4 neurons, with layer-specific mechanisms playing a key role in this process.The article reviews the mechanisms underlying the development and evolution of thalamocortical connectivity in mammals. Thalamocortical axons (TCAs) navigate through the forebrain, crossing boundaries such as the pallial-subpallial boundary (PSPB) and the diencephalic-telencephalic boundary (DTB). The PSPB, in particular, presents a significant challenge for TCAs, with various guidance defects observed in mutant mice. Early thalamocortical projections from subplate neurons and corticofugal axons from the lateral ganglionic eminence (LGE) assist TCAs in crossing these boundaries. The "handshake hypothesis" suggests that these interactions help TCAs navigate through the PSPB. Genetic studies, such as those involving *Emx2* and *Arid1a*, have revealed the importance of transcription factors and subplate neurons in guiding TCAs. TCAs accumulate in the subplate zone during a "waiting" period before invading the cortical plate, where they form transient synapses with subplate neurons. The evolution of the PSPB has significantly impacted thalamocortical connectivity, with changes in genes like *Pax6* contributing to these differences. Thalamocortical activity is crucial for cortical development, influencing the formation of barrels, cytoarchitectonic patterns, and interneuron morphologies. Thalamic regulation also affects cortical neurogenesis and laminar development. The precise targeting of TCAs to specific cortical areas is established through interactions with subplate neurons and L4 neurons, with layer-specific mechanisms playing a key role in this process.