I am very pleased to act as guest editor of this special issue on aptamers for Analytical and Bioanalytical Chemistry. Aptamers started as therapeutic agents and in a very few years they became a hot subject in analytical chemistry as well. In our laboratory we are working mainly in realizing reliable sensors and biosensors, and aptamers appear as optimal components for assembling them by immobilization (a biological mimetic component in this case) for specific biorecognition. Aptamers appear in this application as a new class of ligands with exceptional binding constants (micromolar to picomolar range). In addition, aptamers are also entering into many analytical applications, such as in technologies based on separation science (various chromatographic techniques or capillary electrophoresis), and many new exciting analytical problems can be solved with these new compounds. Owing to the increasing presence of contaminants in food, air or drinking water that are capable of causing intoxication, diseases or chronic illness, the need for analytical systems capable of rapid and often multianalyte measurements of complex samples is rising. This need is also experienced in the medical field, where multiparameter diagnostic systems are increasingly required in order to detect all the well-known and the more recently developed biomarkers for different diseases. When the detection system requires a biomolecular recognition event, antibody-based detection methods are still considered the standard assays in environmental, food and clinical analysis. These assays are well established and they have been demonstrated to achieve the desired sensitivity and selectivity. However, the use of antibodies in multianalyte detection methods and in the analysis of very complex samples could encounter some limitations mainly deriving from the nature and synthesis of these protein receptors. In order to circumvent some of these drawbacks, other recognition molecules are being explored as alternatives. The awareness that nucleic acids, RNA in particular, can assume stable secondary structures and that they can be easily synthesized and functionalized has opened the door to aptamers in several applications. The main advantage is overcoming the use of animals or cell lines for the production of the molecules. Moreover, antibodies against molecules that are not immunogenic are difficult to generate. In contrast, aptamers are isolated by in vitro methods that are independent of animals: an in vitro combinatorial library can be generated and exploited against any target. In addition, generation of antibodies in vivo means that it is the animal immune system that selects the sites on the target protein to which the antibodies bind. The in vivo parameters restrict the identification of antibodies that can recognize targets only under physiological conditions, limiting the extent to which the antibodies can be functionalized and applied. Moreover, the aptamer selection process can be manipulated to obtain aptamers that bind a specific region of the target and with specific binding properties in different binding conditions. After selection, aptamers are produced by chemical synthesis and purified to a very high degree by eliminating the batch-to-batch variation found when using antibodies. By chemical synthesis, modifications in the aptamer can be introduced, enhancing the stability, affinity and specificity of the molecules. Often the kinetic parameters of the Anal Bioanal Chem (2008) 390:987–988 DOI 10.1007/s00216-007-1769-y