Book excerpt: Chemical sensing is likely the most primordial sensory modality that emerged in the evolution of life. Without chemical sensing life on earth would probably not exist. It is used for detecting nutrients, avoiding threats, finding mating partners and various forms of communication and social interaction between animals. The advent of artificial sensors has created a myriad of problems in the areas of chemical detection and identification with applications in food quality and pollution control, chemical threat detection, health monitoring, robot control and even odor and taste synthesis. Efficient algorithms are needed to address the many challenges of chemical sensing in these areas, including (but not limited to) sensitivity levels, sensor drift, concentration invariance of analyte identity and complex mixtures. Defining and improving analysis methods for artificial chemical sensing remains an active research area in engineering and machine learning alike. In the course of evolution animals, bacteria and plants have developed sophisticated methods and algorithms for solving difficult problems in chemical sensing very efficiently. Complex signalling pathways inside single cells can trigger movement toward the source of a nutrient. Complex networks of neurons appear to be able to compute odor types and the distance to a source in turbulent flows. These networks of neurons use a combination of temporal coding, layered structures, simple Hebbian learning rules, reinforcement learning and inhibition to quickly learn about chemical stimuli that are critical for their survival. Olfaction is a vibrant filed of research because recent technological advances allow monitoring and manipulating brain areas inaccessible in the past thus allowing for rapid progress. This is particularly relevant because to this date the best solutions to many general chemical sensing problems are still found in animals rather than artificial devices. Many lessons may yet have to be learned from biological systems to solve the complex problems of chemical sensing with similar success as animals routinely do. This special issue has the ambitious goal of bringing together biologists and engineers to report on biological solutions and engineering approaches to chemical sensing challenges in order to better understand in what aspects both fields can find common ground of discussion and to thus promote novel areas of interdisciplinary research.