Duplicate content on your site can create many problems for search engines and, by extension, problems for your rankings. You want to avoid duplicate content on your site for three major reasons:

Search engines don’t know which version to include in the index and which ones to exclude.
Search engines don’t know whether to direct all link metrics (which contribute to ranking) to a single page or distribute it between all page versions.
Search engines don’t know which version to rank for search results

All of these issues have the potential to harm the ranking of your pages, according to Moz. Still, with the help of canonical links, you can easily signal to search engines which version of the page you want to be considered the true version of the page. The image below shows an example of what a canonical link would look like in the source code of a page.

What is a Canonical Link?

A canonical link is an element that is included in a page to point search engines to the preferred version of the page. By doing this, search engines know exactly which page the site owner wants to be indexed and ranked over other pages with the same content. This stops the problem of link metrics being improperly distributed and the potential harm to your rankings that comes along with that. Including canonical links in your pages is also important because you can’t always control how other people and sites will link to your pages. Say, for example you have the two following pages on your site:

example.com/practice/injury-lawyers
example.com/injury-lawyers

Both pages have the same content, and other websites have linked to both. Obviously, the content on both is valuable. By setting up a canonical link from one page to the other, you can retain all of the link metrics of that page and have search engines apply it to a master version of the page. Think of it as a sort of consolidation of the value of multiple versions of the same page into a single, more powerful page. Considering that Google’s search engine accounts for the vast majority of searches, it’s best to look over their guidelines for using canonical links as well.

Canonical Link vs. a Full Page Redirect

Many web admins use what’s called a 301 redirect to avoid duplicate content issues. Put simply. A redirect does exactly what it sounds like. When someone navigates to a URL either from a link or by typing it into their web browser, they are redirected to the page that the webmaster wants to be the master copy. The problem with this is that it’s no longer possible to visit the duplicate page. Creating a redirect takes a little more work than canonical linking does. Canonical links will still allow users to visit the page that is considered a duplicate but will still contribute all of the link metrics of the duplicate page to the master page that you want search engines to divert traffic to. Canonical links are also much easier to create as they can be written directly into the HTML of a page.

Routinely Check Your Canonical Links or Hire an SEO Company

You are likely constantly adding new pages to your site. Because of that, there is the constant possibility of new duplicate pages. Keeping on top of duplicate content can be a full-time job in itself. If it seems like more than you’re willing to undertake, then a professional SEO company can take care of it for you. However, you should never neglect this critical aspect of your site because it can cause your pages to rank much worse than they would otherwise.