Ac electrokinetics involves the study of particle movement in suspension under alternating current (AC) electrical fields. This review discusses the forces acting on particles in microelectrode structures, including electrokinetic, electrothermal, and hydrodynamic forces. The development of microfabricated electrodes has enabled manipulation of particles as small as macromolecules, but other forces, such as electrothermal and hydrodynamic effects, also influence particle behavior. High electrical fields required for particle movement lead to heat dissipation, creating thermal gradients that induce fluid motion through buoyancy and electrothermal forces. The paper analyzes the frequency dependence and magnitude of electrothermally induced fluid flow, identifying a new type of fluid flow at low frequencies. Brownian motion, diffusion, and buoyancy forces are discussed in the context of sub-micrometre particle manipulation. The relative influence of these forces on particle behavior is evaluated, with calculations showing the orders of magnitude of forces experienced by sub-micrometre particles. Experimental observations demonstrate that dielectrophoretic (DEP) forces, electrothermal forces, and hydrodynamic forces all play roles in particle movement. The DEP force is calculated using the Clausius-Mossotti factor and the electrical field gradient. Electrothermal forces are analyzed using power dissipation and temperature rise calculations, showing that high conductivity media can lead to significant temperature increases. The paper also discusses electrothermal forces, including Coulomb and dielectric forces, and their effects on fluid motion. The results show that electrothermal forces can dominate over DEP forces under certain conditions. The paper concludes that microelectrode technology is essential for low-temperature dielectrophoresis, particularly for sub-micrometre particles. The analysis of fluid flow and temperature effects provides insights into the complex interactions between electrical and thermal forces in microelectrode systems.Ac electrokinetics involves the study of particle movement in suspension under alternating current (AC) electrical fields. This review discusses the forces acting on particles in microelectrode structures, including electrokinetic, electrothermal, and hydrodynamic forces. The development of microfabricated electrodes has enabled manipulation of particles as small as macromolecules, but other forces, such as electrothermal and hydrodynamic effects, also influence particle behavior. High electrical fields required for particle movement lead to heat dissipation, creating thermal gradients that induce fluid motion through buoyancy and electrothermal forces. The paper analyzes the frequency dependence and magnitude of electrothermally induced fluid flow, identifying a new type of fluid flow at low frequencies. Brownian motion, diffusion, and buoyancy forces are discussed in the context of sub-micrometre particle manipulation. The relative influence of these forces on particle behavior is evaluated, with calculations showing the orders of magnitude of forces experienced by sub-micrometre particles. Experimental observations demonstrate that dielectrophoretic (DEP) forces, electrothermal forces, and hydrodynamic forces all play roles in particle movement. The DEP force is calculated using the Clausius-Mossotti factor and the electrical field gradient. Electrothermal forces are analyzed using power dissipation and temperature rise calculations, showing that high conductivity media can lead to significant temperature increases. The paper also discusses electrothermal forces, including Coulomb and dielectric forces, and their effects on fluid motion. The results show that electrothermal forces can dominate over DEP forces under certain conditions. The paper concludes that microelectrode technology is essential for low-temperature dielectrophoresis, particularly for sub-micrometre particles. The analysis of fluid flow and temperature effects provides insights into the complex interactions between electrical and thermal forces in microelectrode systems.