The 900 µm droplets are coated with Au-Fe 3 O 4 nanosurfactants and, initially (00:00 – 00:06s) are randomly distributed and spaced by, on average, several millimeters. When light (660 nm, 70 mW) irradiates one of the droplets (00:07s), the other droplets move rapidly toward the irradiated locus, forming a two-dimensional, closely-packed structure in less than 10s. Next, sequential light-driven assembly / spontaneous disassembly cycles are demonstrated (00:17 - 02:16s). Initially, the laser light is off and the droplets are randomly distributed (00:17s). When the laser is turned on (00:18s), droplets approach the irradiated spot, forming a bilayer aggregate (00:19 - 00:37s). The droplets in the bottom layer locate into the triangular gaps of the upper layer. When the light is off (00:38s), the ordered structure disassembles by thermal diffusion (00:37 - 00:57s). When the light is back on (00:58s), a compact structure forms again (00:58 - 01:12s). When the light is off (01:13s), the structure disassembles (01:13 - 01:21s). When the light is again on (01:21s), droplets assemble again (01:21 - 01:46s). When the light is off (01:47s), the ordered structure disassembles (01:47 - 02:03s). Finally, when the light is on, an ordered structure is yet again assembled (02:03 -02:16s). Light-induced assembly of droplets into a three-dimensional closely-packed structure (02:16 - 02:59s). The droplets are coated with Au-Fe 3 O 4 nanosurfactants. The diameter of the droplets is ~ 500 µm. The laser light (660 nm, 70 mW) irradiation starts at (02:17s). The size of the assembled structure first increases to ~5 mm (02:17-02:47s) and then remains roughly constant (02:48 - 02:59s). Note that some droplets at the border of the aggregate are in equilibrium with the aggregate and detach/reattach to it. (MP4 15297 kb)