It is evident that until one knows what information needs to be presented at the listener's ears, no rational system design can proceed.Michael A. Gerzon 1976 and AES Vienna [1] 1992. Abstract This chapter describes the perceptual properties of auditory events, the sound images that we localize in terms of direction and width, when distributing a signal with different amplitudes to one or a couple of loudspeakers. These amplitude differences are what methods for amplitude panning implement, and they are also what mapping of any coincident-microphone recording implies when reproduced over the directions of a loudspeaker layout. Therefore several listening experiments on localization are described and analyzed that are essential to understand and model the psychoacoustical properties of amplitude panning on multiple loudspeakers of a 3D audio system. For delay-based recordings or diffuse sounds, there is some relation, however, it is found to be less stable for the desired applications. Moreover, amplitude panning is not only about consistent directional localization. Loudness, spectrum, temporal structure, or the perceived width should be panning-invariant. The chapter also shows experiments and models required to understand and provide those panning-invariant aspects, especially for moving sounds. It concludes with openly-available response data of most of the presented listening experiments. Starting from classic listening experiments on stereo panning by Leakey [2], Wendt [3], and pairwise horizontal panning by Theile [4], this chapter explores the relevant perceptual properties for 3D amplitude panning and their models. Important experimental studies considered here are for instance those by Simon [5], Kimura [6], F. Wendt [7], Lee [8], Helm [9], and Frank [10, 11]. By the experimental results, it