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The presence of harmful algal blooms (HABs) can result in the accumulation of phycotoxins in shellfish such as mussels, scallops and oysters. Depending on the toxins present, consumption of contaminated shellfish can lead to illness in humans including amnesic, diarrheic or paralytic shellfish poisoning (ASP, DSP or PSP respectively). There is currently a lack of suitable rapid screening tools to complement accepted reference methods for the detection of marine biotoxins. The aims of the thesis were to develop a range of simple and accurate lateral flow immunoassays (LFIA) for the rapid screening of phycotoxins from shellfish extracts, which could be performed either in a laboratory or in the field. As a result, three novel single-step LFIAs were developed and validated for the major regulated toxins responsible for ASP, DSP and PSP, respectively. One of the challenges was to ensure that the thresholds for test~ were based at concentrations relevant to regulations, whilst minimizing the risks of generating positive results from samples deemed compliant to regulations. Qualitative results (negative/positive) were generated using a portable reader to remove subjectivity from results interpretation. Rapid and simple procedures were devised whereby samples could be reliably screened in parallel for key toxins (DA, OA, DTX1, DTX2, STX, NEO, GTX1&4, GTX2&3, dcSTX, dcNEO, dcGTX2&3, C1&C2, GTX5) in 20 min, including sample extractions. To include detection of DTX3 esters, a hydrolysis procedure could be incorporated into the procedure. Validations consisted of evaluating performance characteristics such as accuracy, sensitivity, cross reactivity, stability and robustness/ruggedness. Intra- and inter- laboratory evaluations demonstrated that key toxins could be accurately detected from a variety of shellfish samples (spiked and naturally contaminated) and included comparisons with reference methods.