POA is Partial Order Alignment, a fast program for multiple sequence alignment (MSA) in bioinformatics. Its advantages are speed, scalability, sensitivity, and the superior ability to handle branching / indels in the alignment. Partial order alignment is an approach to MSA, which can be combined with existing methods such as progressive alignment. POA optimally aligns a pair of MSAs and which therefore can be applied directly to progressive alignment methods such as CLUSTAL. For large alignments, Progressive POA is 10-30 times faster than CLUSTALW.