This talk will explore how the physics of the superconductor–insulator transition (SIT) can be leveraged for new approaches to designing and developing superconducting quantum circuits. The SIT is a fundamental quantum phase transition governed by quantum, rather than thermal, fluctuations. On the superconducting side of the transition, the phase of the local order parameter serves as the good quantum number, enabling Cooper pairs to flow without resistance. On the insulating side, the conjugate variable — charge — becomes the good quantum number, and vortices flow freely. Superconducting qubits are circuits with one degree of freedom that similarly exhibit regimes where either charge or phase is a good quantum number. Just as charge–phase duality underlies the SIT, it also lies at the core of superconducting qubits, giving rise to dual architectures such as the transmon and the blochnium qubit. This talk will show efforts to engineer qubits from materials tuned near their SIT, where nanoscale weak links naturally emerge and provide the nonlinearity required for qubits—demonstrated here in devices built from a single film of niobium nitride. Finally, I will discuss how these same junctions, that are the building blocks of superconducting qubits, can be fabricated into networks to serve as a steppingstone to realize solid-state quantum simulators and study interacting many-body systems such as the Hubbard model.