Polymeric nano and microparticles are important tools for an increasing variety of applications in the life sciences such as cellular delivery, sensing and imaging, with a fundamental requirement being particle functionalisation. Herein, the use of zeta potential measurements is described as a convenient tool to allow a variety of chemical reactions to be rapidly monitored on particles. To allow multifunctionalisations these particles need to be orthogonally modified. As part of this thesis, novel dual-functionalised aminomethyl and boronic acid particles were synthesised. These particles could be modified via amide formation and palladiummediated cross coupling, with applications demonstrated in cellular delivery and cellbased cargo release. The requirement for bright fluorescent particles for applications in the life sciences was addressed by the synthesis and analysis of particles prepared using polymerisable fluorescein derivatives. Although nanoparticles are a promising technology to solve a variety of problems, their behaviour in biological systems is not fully understood. Herein, the effects of the particle’s surface chemistry on cellular uptake and toxicity were investigated.