A Y-STR is a short tandem repeat (STR) on the Y chromosome. Y-STRs are usually designated by DYS numbers. The standard Y-chromosome (Y-DNA) test used for genealogical purposes looks at Y-STRs, called Markers.
Y-STR allele nomenclatures
DNA testing companies or labs in certain cases use different nomenclatures to designate the same Y-STR allele. Thus, a conversion must be applied in these cases to accurately compare Y-STR results obtained from different companies. The most common nomenclature is based on guidance provided by NIST for Y-STR markers historically reported differently by various companies. The NIST standard is the proposal of ISOGG for genetic genealogy companies. 
- from FTDNA to NIST: In FTDNA Projects the Haplotypes (STR Values) are formatted in the FTDNA lab standard (v1 until 2008, v2 since 2009?). For conversion from FTDNA v2 to NIST (ISOGG) standard used in scientific studies the following conversion apply:
DYS441 +1, DYS442 +5, YGATAA10 +2, GATA H4.1 +1.
- from NIST to FTDNA: DYS441 -1, DYS442 -5, YGATAA10 -2, GATA H4.1 -1. Sometimes DYS389II-I is listed; both values need to be summed.
- from ISFG to FTDNA: same as for NIST except for GATA H4.1 -10 (-9-1)
Y-DNA STR Haplotype Databases
The following is a list of databases containing publicly submitted surnames and Y-STR haplotypes:
- National Institute of Standards and Technology (NIST) standard reference database
- National Institute of Standards and Technology (NIST) (US) — Y STR Positions along Y Chromosome
- National Institute of Standards and Technology (NIST) — Summary List of Y Chromosome STR Loci and Available Fact Sheets
- National Institute of Standards and Technology (NIST) — STR Fact Sheets
- National Institute of Standards and Technology STR training materials
- "Marker Standards". Sorenson Molecular Genealogy Foundation. http://www.smgf.org/ychromosome/marker_standards.jspx. Retrieved 11 August 2012.
- Gale Matthiesen, Diana (19 July 2011). "Converting Y-DNA STR Test Results between SMGF, AncestryDNA, and FamilyTreeDNA". http://dgmweb.net/DNA/General/ADNA_FTDNA.html. Retrieved 11 August 2012.
- SMGF marker standards
- Molgen Forum discussion, Aug 2012
- SMGF Y-chromosome search
- Genebase Y-STR marker types tutorial
- List of DYS markers
- Y-DNA Testing Company STR Marker Comparison Chart
- Y-STR allele frequencies by haplogroup, a resource compiled by the late Leo Little
- Matching multicopy Y-STR markers in closely related individuals A presentation by Thomas Krahn of Family Tree DNA]
- An Interview with John Butler and the Human Identity Group of U.S. NIST Journal of Genetic Genealogy, Fall 2008, Volume 4, Number 2.