<p>Engineered nanoparticles have greatly expanded cancer treatment by encapsulating and delivering therapeutic and diagnostic agents, otherwise limited by poor pharmacokinetics and toxicity, to target tumour cells. Leveraging our increased understanding of the tumour microenvironment, nanomedicine has expanded to additionally target key tissues and cells implicated in tumorigenesis, such as immune and stromal cells, to improve potency and further mitigate off-target toxicities. To design nanocarriers that overcome the body’s physiological barriers to access tumours, the field has explored broader routes of administration and nanoparticle design principles, beyond the enhanced permeation and retention effect. This Review explores the advantages of non-covalent surface modifications of nanoparticles, along with other surface modifications, to modulate nanoparticle trafficking from the injection site, into tumour and lymphoid tissues, to the target cell, and ultimately its subcellular fate. Using electrostatic or other non-covalent techniques, nanoparticle surfaces can be decorated with native and synthetic macromolecules that confer highly precise cell and tissue trafficking. Rational design can additionally minimize detection and clearance by the immune system and prolong half-life — key to maximizing efficacy of therapeutic cargos. Finally, we outline how cancer nanomedicine continues to evolve by incorporating learnings from novel screening technologies, computational approaches and patient-level data to design efficacious targeted therapies.</p>