FamilyTreeDNA has been expanding their SNP Packs greatly since their introduction earlier this year. They now offer over 70 different SNP Packs after having started the summer of 2016 with around 45 and having none at the start of 2015.

SNP Packs can be a great cost saving over BigY. $120 for an SNP Pack versus $575 or more for BigY. But the SNP Pack does dramatically reduce the result — only a hundred SNP values returned versus 20,000 to 50,000 for BigY. But if many members in a matching STR group already have tight STR matching, then there is no strong requirement for everyone to do BigY. Instead, the one or more that have done BigY can be used to figure out if there is an SNP Pack that covers their groups terminal / leaf haplogroup on the Phylogenetic Tree and other SNPs of branch points nearby. If so, members who have not done BigY can simply order the appropriate SNP Pack. If they are matching the BigY results of the others in the group, they can simply ride on the coat-tails of the BigY testers that they share the STR values with. While this does not allow the determination of nearer-term (time) novel variants that may be unique to a family line, it does allow the membership in the surname group and STR haplotype to be decisively confirmed.

BigY is helping expand the knowledge of yDNA SNPs and finding even recent, private SNP's in family lines, But often, members of a group are just looking to confirm that their STR match into a surname group is a true match and not just a convergence of STR values with some other line. Testing with an SNP Pack, determined for a family branch from anothers' BigY result can get this confirmation without the expense of BigY. See each family groups DNA page for more information on the appropriate SNP Pack to use. Converged STR haplotypes should have different haplogroups indicated in BigY and similar deep yDNA SNP tests.

FamilyTreeDNA does not identify clearly the area of the phylogenetic tree each SNP Pack covers. They simply identify the SNP Pack by branch point SNP name. But that name might not be commonly known. As a result, we developed and maintain a mapping of SNP Packs to ISOGG / YCC long path names and a yFull tree link; for everyone's convenience. See our Google Spreadsheet for the most up to date listing. When at the SNP Pack order list, if you click on the pack name, it will expand to list all the SNPs covered by the test.

UPDATE: We added our own Tutorial on Ordering SNP Packs!
FamilyTreeDNA makes it very difficult to find the SNP Pack list and thus select the specific one to order. See the WorldFamilies post description of ways to get to the SNP Pack order list. UPDATE: It is reprinted here as the WorldFamilies site is now going offline as of May 2018.
  • You can order these tests by clicking on the blue Upgrade button in the upper right corner of your FTDNA Dashboard page, then clicking on the blue Buy Now button under Advanced Tests on the left hand of the subsequent screen. In the filter, select SNP Packs and the 13 should appear. You can also click on the Y-DNA Haplogroup flag in the upper right corner or the Haplotree & SNPs button under the Y-DNA section of your Dashboard page to call up the FTDNA Haplotree. Scroll all the way to the bottom of that page until you see blue hyperlink that says "advanced SNP order form." Change the Filter from SNP to SNP Pack and you will see the 13 tests.
The link also offers a nice commentary of the SNP Pack development over a few year period.