A method of manufacturing a panel, the panel comprising a composite skin and at least one composite stiffener, the method comprising: positioning first and second mandrels on opposite sides of the stiffener; positioning first and second compaction tools on opposite sides of the skin; and compacting the skin between the first and second compaction tools by moving one or both of the compaction tools, wherein the movement of the compaction tool(s) causes the first and second mandrels to move towards the stiffener along inclined paths so as to compact the stiffener between the mandrels.