Haplogroup I1 and Haplogroup I-M253 are synonyms.

Haplogroup I1 has an estimated time to most recent common ancestor around 4000 to 5000 years, and the haplogroup is commonly denoted as I-M253, where M253 being one of the 300 SNP mutations defining the haplogroup.
While many men belonging to I1 have traced their paternal lines in northern Europe, the haplogroup is also present in all European countries at lower shares.
Anyone that tested an STR test (Y12/Y37/Y67/Y111) and got the haplogroup result I-M253 is welcome to join this project. Also welcome is anyone who made more advanced SNP tests such the BigY or SNP packs and belongs to to any haplogroup subclade under I-M253.
Noteworthy, this project is focused on studying the haplogroup I1. We do not welcome Y-testers belonging to other main haplogroups, such as R, E, N etc. Also, we do not welcome Y-testers belonging to haplogroup I2 or I root. If joining without belong to haplogroup I-M253, your membership will get cancelled.


How do I know I am I1? Because all men with the M253 y-chromosome SNP share a common ancestor all of their short tandem repeat markers, STRs, can be expected to be in a range around that of their forefather. It is then possible to predict the probability of someone's M253 status based on the frequency of their STR values among known I1s. Haplogroup predictions are done by the software at FTDNA and by Whit Athey's Haplogroup Predictor. (DYS455=8 is a very good predictor).  It is also possible to do the math by hand. This table shows the STR value distribution based on the 454 unique haplotypes from the first panel of markers. You may then look at your prediction by FTDNA, use the Whit's Predictor, and compare the frequencies of your marker results to other I1s. In most cases all of these methods will be in agreement and testing for M253 is unnecessary for both genealogical and anthropological information. If you still have doubts, you may wish to look at Borges' article 'Why SNP' to decide if a SNP test is right for you.
The most likely reason for an I1 to take a SNP test is to check for the  M253 subclade SNPs, DF29, CTS6364, L22, Z58, Z63, Z131. More often than not, it is better for an I1 to order SNP's a la carte, rather than ordering the outdated Deep Clade test. Big Y has been shown to be extremely useful in bringing the haplotree to light.  Before ordering SNP's, you might want to ask an administrator for advise.

Project placement of members results
After you have joined the project, your results will get automatically and temporarily placed under the category 'Ungrouped'.
Shortly thereafter, usually within 2-3 days, but often faster, your kit will get sorted into a new category header, given that you have assigned access to your results to project administrators and given that you have signed the release form of your account.
If you have tested BigY your kit will get placed by administrators in a subcategory header according to your test result, also meaning your result is placed among Y-testers that have the most close patrilinear relationship to you.
In case you only have tested STR tests Y12 or Y25 your test result will typically be placed in category header for Y12/Y25 kits at the end of the result pages. We will typically not make any subclade prediction for kits with so few STRs being tested. Subclade predictions based on so few STR are typically not very reliable.