Sensors for the determination of fluid and gas properties are being employed for direct and indirect condition monitoring in many application areas of instrumentation and automation. This article presents various robust sensors devised to measure flow properties (velocity, direction, and mass flow) as well as thermal properties (thermal conductivity and diffusivity) of fluids. These sensors are based on a thermal operation principle and can be manufactured with cost-effective microtechnology. Starting from one generic design, they can be implemented and operated as calorimetric flow sensors or thermal conductivity sensors. This article explains the theoretical foundations and discusses several application examples.