An Author ID is a unique identifier used to distinguish you from other researchers who have the same or similar names. Using an author ID can help ensure that all of your publications and research are associated with your profile in databases or online. Signing up for author IDs and making sure that you use them in your C.V. and website is something all researchers should do to make their work more findable and identifiable.
There are several author ID schemes. Below we outline ORCID, Scopus ID, Researcher ID, and Google Scholar profiles, which are all used across disciplines. There are also several discipline-specific ID schemes.
What is it?
ORCID (Open Researcher and Contributor ID) is an open, non-profit system to provide unique identifiers to researchers working in all fields. It is rapidly becoming a cross-disciplinary standard, and it works with other ID systems as well, which means it can connect different research systems and save you time on entering data.
How to get one
Go to http://orcid.org/ and click "register now" to obtain an ORCID.
What it's used for
List your ORCID on your C.V., your web profile, your grants, and anywhere else you provide a list of work.
How to improve your profile and correct errors
Some publications will be automatically loaded when you sign up for ORCID. You can also manually add publications and other information; when you sign in, you will have a chance to add publication and other biographical information. You can also add your SCOPUS author ID, ResearcherID , import from Google Scholar (see below) and publications association with these IDs will be automatically loaded.
What is it?
SCOPUS is a database of literature from all fields, produced by Elsevier. The database automatically assigns unique ID numbers to authors. These IDs help SCOPUS distinguish between similarly-named authors as well as helping to group all the documents by an author together.
How to get one
If you have publications indexed by SCOPUS, you have automatically been assigned a SCOPUS author ID number. You can find this by going to: http://www.scopus.com/search/form/authorFreeLookup.url and entering your information.
What it's used for
In addition to being the tool SCOPUS uses to identify authors, some grant agencies will ask you for SCOPUS ID numbers.
How to improve your profile and correct errors
If there are errors in your profile, you can fill out the author feedback form: in SCOPUS, run an author search, click on the author's name, then on the link that says "request author detail corrections."
You can add your SCOPUS ID to your ORCID profile by clicking "add to ORCID" from your author page in SCOPUS; directions are here. Once you do this, you will be asked to log into ORCID, to verify that you authorize SCOPUS to access your ORCID account, and then you will walk through adding the appropriate SCOPUS profile and publications to your ORCID profile.
If you have publications indexed in Google Scholar, you can create a profile that will show up when people search on your name. It will display your publications, any information you provide, and a set of metrics including h-index.
Go to http://scholar.google.com/citations and sign in with your Google account. You will then be asked for your name, affiliation, etc. Next, Google Scholar will automatically suggest publications to add to your profile. Select the ones that are yours to add to your profile. Add your research interests as keywords, which can then be used to search on by people looking for other researchers in a field.
A Google Scholar profile will show up at the top of results when people search for your publications in Google Scholar. It increases visibility of your work by providing a bibliography, indicates which publications are yours if you share a common name. It also shows a citation count to your work, provides an H-index measure.
See Google's FAQ for answers to how to add missing publications or correct other errors.
What is it? 
Researcher ID is a unique identifier scheme developed by Clarivate and used in Web of Science as well as being compatible with other ID schemes.
How to get one
Go to http://www.researcherid.com/ and click "join now", and enter your information. You will be sent an email; click on the link in the email and finish entering your information (such as your institution name) to create the ResearcherID. You will then be able to link the ID to ORCID.
What it's used for
ResearcherID, like ORCID and SCOPUS author ID, is used to tell authors with similar names apart and produce profiles of author work. If you use Endnote or Web of Science, ResearcherID ties into these systems seamlessly. Use your ResearcherID on your CV, grants, and other profiles.
How to improve your profile and correct errors
Once you have gotten the ResearcherID, you can add to your publications list by clicking "add publications" and then searching Web of Science, adding a RIS file from Endnote or RefManager, or connecting directly to Endnote. You can also connect to ORCID, and import the publications from your ORCID profile (or vice-versa).
Parts of this guide were borrowed and/or adapted from resources from the UC Davis Libraries. Thanks for sharing!