Rapid tests that are low-cost and portable are the first line of defence in healthcare systems. Dipstick and lateral-flow are the two universal assay formats as they are lightweight and compact, and provide qualitative results without external instrumentation. However, existing formats have limitations in the quantification of analyte concentrations. Hence, the demand for sample preparation, improved sensitivity and user-interface has challenged the commercial products. Recently, capabilities, sensors and readout devices were expanded to multiplexable assays platforms, which might transcend the capabilities of existing design format of diagnostic tests. This chapter outlines the evolution of diagnostic devices and current trends in the development of qualitative and quantitative sensing devices for applications in healthcare, veterinary medicine, environmental monitoring and food safety. The chapter also discusses design parameters for diagnostics, their functionalisation to increase the capabilities and the performance, emerging sensing platforms and readout technologies. The factors which limit the emerging rapid diagnostics to become commercial products are also discussed.