Why does a quantum measurement yield one definite outcome rather than another? Decoherence theory explains the disappearance of interference, yet it leaves the selection of a particular result unexplained—and says nothing about what role, if any, the observer plays. This paper confronts both gaps head-on. We construct an Extended Hilbert Space HTotal=HPhys⊗HHigher in which information-processing agents carry their own quantum degrees of freedom, coupled to the physical sector through an explicit interaction Hamiltonian. The resulting Intention Field Theory (IFT) draws on von Neumann’s two-process picture and Stapp’s arguments for mental causation, but goes further by deriving—rather than postulating—a Lindblad-form master equation from the coupling term. Four results follow: agent-dependent decoherence rates that scale with intentional coherence; observer-dependent corrections to Born-rule probabilities; preferred-basis selection fixed by the measurement interaction; and an entropic quantification theorem linking intentional coupling to entropy production, physical–higher mutual information, and a Landauer heat-dissipation bound per measurement event. We test these predictions against eleven landmark experiments—quantum Zeno, which-path, delayed-choice, Bell-inequality, and matter-wave platforms among them—and find per-event entropy increases spanning 10−14 to 10−1 bits, depending on coupling strength and interaction time. When the intentional coupling is switched off, every prediction collapses back to standard quantum mechanics, so the framework is conservative by construction. We compare IFT with nine major interpretations and several dynamical-collapse models, map out the theory’s current limitations, and design specific falsification protocols. The mathematical development is deductive: axioms first, then lemmas, propositions with full proofs, and finally testable corollaries whose numerical signatures differ from those of all existing frameworks.