This thesis is principally concerned with the synthesis of a range of thiourea and guanidinium based receptors and their binding properties with carboxylates. Chapter 1 provides an introduction to the thesis and discusses, in the main part, the binding of monocarboxylates by synthetic receptors. Chapter 2 describes a range of thioureas and investigates in detail their binding with acetate via a range of techniques. A discussion of the enthalpic and entropic elements of their binding and the effect of preorganisation via intramolecular hydrogen bonding is also included. The addition of two amide-carboxylate hydrogen bonds results in a 50 fold increase in complex stability over 1,3-dimethylthiourea (G ≈ 9 kJ mol⁻¹). Chapter 3 describes a family of guanidinium based receptors, analogous to the thiourea discussed in chapter 2. The binding of acetate in DMSO-d₆ is presented and evidence for significant increase in complex strength on preorganisation of the host via intramolecular hydrogen bonding to a pyridine nitrogen lone pair is reported (G ≈ 3.5 kJ mol⁻¹). Chapter 4 describes work towards a rationally designed tweezer receptor based on the simple architectures described in chapter 3. Unfortunately, insolubility of the tweezers prevented evaluation of their binding properties with tripeptide guests.