Planet formation is the process where dust grains grow to pebbles,
planetesimals, and rocky planets or cores of gas giant planets in
protoplanetary disks. The process as well as the planetary properties
such as masses can be imprinted in disks, thus obtaining the detailed
disk structure is central to understand how the planet forming activity
proceeds in the entire regions of the disks. I will review the recent
results of disk observations mainly with the Atacama Large
Millimeter/submillimeter Array (ALMA). The fine disk
structures/substructures have been resolved with about 5-au resolution
of ALMA in dust continuum, and those images often show that the disks
consist of concentric annuli, or sometimes show the spiral arms or
strong non-axisymmetry. Combined also with the gas observations,
plausible mechanisms to explain those structures include the trapping of
dust particles at the local pressure maxima and the disk-planet
dynamical interaction.