I understand that practitioners who e-file must have a tracking number to be able to e-file. How do you obtain this number?

[IntuitAlicia]

Maybe it's an ETIN you're running across.  If so, that's the Transmitters number.  When sending an e-file to the IRS through a software program, that program acts as the Transmitter.

[TAXOH · Accepted solution]

It's called an EFIN and you get it from the IRS. 

[AshleyatIntuit]

IRS issues "tracking numbers" on your efin documentation (Application Summary) which may be what you're referring to, but TAXOH is correct, the EFIN is your main concern.  

[klpontiff]

I have already have an EFIN number, but I am told that for the 2018 filing season, a "tracking number" will be required by IRS to be able to e-file.

[garman22]

Have you searched IRS website re: this "tracking number"? An EFIN is what one needs to efile which you state you already have. You are not talking about a "submission id #" are you?

[George4Tacks]

I think the e-file also records the MachineID which is specific to the computer the file is generated from. This is not new for 2018. Whatever it is, I am sure we all have one so that IRS can chase down all the bad guys that are filing fraudulent returns. I you are one of the good guys, don't worry about it. 

Each return used to have DCN (Document Control Number) a few years ago that became the Submission ID. https://www.irs.gov/e-file-providers/ero-duties-after-submitting-the-return-to-the-irs