The key features of AliView include the ability to swiftly handle large alignments with low memory impact (see Table 1 for comparison with other popular free cross-platform alignment viewers). AliView loads large alignment files 2–14 times faster and demands less than half of the memory resources than comparable alignment editors (Table 1; Supplementary Table S1A–C). AliView will read unlimited size alignment files in FASTA, Phylip, Nexus, Clustal and MSF-format (Table 2). This works through an indexing process where the sequences in the file initially are indexed and only cached in memory when viewed. Aside from the built-in indexing of large files, the program also reads and saves Fasta index files (.fai) as implemented by Samtools (Li et al., 2009). The program either reads the whole alignment into memory or leaves parts on file, depending on memory resources available on the specific computer. This way any alignment file can be opened regardless of the memory resources of the computer.