Flexbox is a one-dimensional layout method for arranging items in rows or columns. display: flex on the container. Items become flex items with default min-width: 0 behavior.
Main axis alignment: justify-content (flex-start, center, space-between, space-around, space-evenly). Cross axis: align-items (flex-start, center, stretch, baseline).
align-self overrides align-items for individual items. flex-grow, flex-shrink, and flex-basis control item sizing. flex: 1 shorthand sets grow:1, shrink:1, basis:0.
flex-direction: row | column | row-reverse | column-reverse controls layout direction. flex-wrap allows items to wrap to multiple lines.
Order property reorders items visually without changing DOM order. This is powerful for responsive layouts where item order should change at different breakpoints.