This paper presents new insights in interaction mechanisms between small particles under the influence of a strong acoustic field. These mechanisms are associated with acoustic agglomeration, an effect that causes relative motion and collisions between fine particles entrained in gaseous media. The agglomeration process has potential use in air pollution control to enhance the performance of conventional particle filtering devices in the fine particle size range. In Sec. I of this paper, a number of existing acoustic agglomeration models are reviewed and implemented into a numerical scheme. A quantitative analysis of the proposed theories is conducted with parameters representing those of the experimental Sec. II. Simulations based on the scattering, orthokinetic, and hydrodynamic agglomeration principles generate numerical trajectories which reflect their importance in the particle interaction process. Most importantly it is shown that a hydrodynamic effect based on asymmetric flow fields around the particles (acoustic wake effect) generates significant particle attraction in the direction of the acoustic velocity vector. To evaluate these theoretical findings, Sec. II of this paper presents new experimental observations of microscopic particle trajectories in an intense acoustic field. The experiments are carried out in a small-scale observation chamber using a CCD camera in conjunction with a high-resolution video system. A homogeneous acoustic velocity field is generated by two rectangular, flat-membrane loudspeakers which comprise two opposing walls in the observation chamber. Glass microspheres (diameters 8.1 and 22.1 μm) and arbitrarily shaped, quartz particles (diameter <50 μm) are used for the observation of interaction and agglomeration trajectories under the influence of an intense acoustic velocity field (1.2–0.53 m/s @400–900 Hz, respectively). The recorded digitized images show a number of different interaction phenomena as well as one distinct pattern that resembles the shape of a tuning fork (thus called the tuning fork agglomeration). The latter appears to be the predominant agglomeration mechanism leading to rapid particle approach and multiple, subsequent particle interactions at large acoustic velocities.