- Go to https://developer.apple.com/programs/ios/
- Click 'Enroll Now'
- Click 'Continue'
- Click 'Create an Apple ID'. If you have an existing Apple ID and don't mind sharing it with us, select 'Sign in with your Apple ID'.
- If you chose to create a new Apple ID, follow the simple on-screen directions to create your new Apple ID.
- Choose whether you are enrolling as an individual or company . If you are a company skip down to the As a Company heading. Otherwise, click 'Individual' and click 'Continue'.
- Enter your billing name and address. Click 'Continue'.
- On the 'Select your program' screen, select iOS Developer Program. Click 'Continue'.
- Review your enrollment information. Click 'Continue'.
- Review the 'Program License Agreement', and check the box confirming your agreement, then click 'I Agree'.
- Click 'Add to Cart', then click 'Check Out Now'
- Enter your Apple ID again to confirm the $99 charge to join the Apple iOS Developer Program.
- Confirm your Shipping Details, click 'Continue'.
- Confirm your Payment Details, click 'Place Order'
- You will receive a confirmation email from Apple for your transaction with a subject line of 'Your order is being processed'. **Note: This is not the activation email**
- Within 24 hours you will also receive an activation email from Apple Developer Program Support.
- In the activation email, click the 'Log-in now' button to navigate to the Apple Developer Center. Congrats! You're done.
As a Company
- If you are an agent of the company who is signing up, choose option A. If you are the owner/founder of the company, choose option B. Click 'Continue'
- Enter your organization details and click 'Continue'. 
- Resume at step 7 above
: If you're unsure which to choose, here's a great article outlining the difference: http://developmylifellc.com/2011/03/02/questions-about-joining-the-apple-developer-program/ Essentially, sign up as an individual if you want to accept payments through your social security number. If you are a company and don't want income passing through you personally, go the 'Company' route. Also, an individual or company name will show as the owner under your app name in the App Store.
: If you need to look up your DUNS number (probably), go to this lookup tool Apple provides at https://developer.apple.com/ios/enroll/dunsLookupForm.action. For more info on what a DUNS number is, go here: https://developer.apple.com/support/D-U-N-S/