AbstractPorous organic polymers (POPs) have gained tremendous attention owing to their chemical tunability, stability and high surface areas. Whereas there are several examples of fully conjugated two‐dimensional (2D) POPs, three‐dimensional (3D) ones are rather challenging to realize in the absence of structural templates. Herein, we report the base‐catalyzed direct synthesis of a fully conjugated 3D POPs, named benzyne‐derived polymers (BDPs), containing biphenylene and tetraphenylene moieties starting from a simple bisbenzyne precursor, which undergoes [2+2] and [2+2+2+2] cycloaddition reactions to form BDPs primarily composed of biphenylene and tetraphenylene moieties. The resulting polymers exhibited ultramicroporous structures with surface areas up to 544 m² g⁻¹ and very high CO₂/N₂ selectivities.