You can sign up for a free 30-day trial if you haven't tried Kindle Unlimited before.

Note: To sign up for the free trial, you must have an Amazon account with a current, valid credit card. 
To be eligible you must be a U.S. resident. 
Also, you need 1-Click payments enabled. Go to Manage 
		Addresses and 1-Click Settings to turn this on.

1. Visit the Kindle Unlimited page.
2. Select Start your 30-day free trial.
3. Sign in with your Amazon account. If you don't have an account, you'll be asked to create one.
4. Follow the on-screen instructions.

While you won't be charged during your free trial, you will be automatically upgraded to a paid subscription plan at the end of the trial period.

You can avoid the upgrade by following the directions in Manage or Cancel Your Kindle Unlimited Membership.
Amazon.com Help: Sign Up for the Amazon Kindle Unlimited Free Trial
 

90 day free trial for existing Prime Members

3 Months (Deal) $29.97 $0.00
Renews at $9.99/month afterwards. Deal expires on 07/31/2019.
Exclusive for Prime members. Deal Terms and Conditions Deal Terms and Conditions.
Start your free trial

By signing up, you agree to the Kindle Unlimited Terms Kindle Unlimited Terms and authorize us to charge your default payment method or another payment method on file after any applicable free trial.
Your Kindle Unlimited membership continues until canceled. If you do not wish to continue for $9.99/month + any taxes, you may cancel anytime at http://www.amazon.com/kucentral/?&_encoding=UTF8&tag=tzmc-20 .