This category is about ballot access in general.
The right of access to the ballot is not absolute. There are restrictions placed on that access based on state laws and party rules. Generally speaking, these state laws define how candidates get on the ballot and the process that political parties and candidates must adhere to achieve ballot access. Technically, everyone has the right to compete to get on the ballot, but they have to do so within certain restrictions.
The state laws work with party rules to define how candidates get access. It is a complicated quagmire. In Illinois, the state assumes everyone should have access and provides different ways that access is achieved. The party rules are framed by Illinois election code.
In Illinois we have three stages for major political parties (Rep’s and Dem’s and in some counties the Greens) to gain access to the ballot. (There are separate processes for third party candidates and for new party candidates.) In the Primary, any candidate who files on time, and survives potential challenge to their filing will get on the ballot to run. If the initial filing period is missed before the Primary, candidates can run as a write-in candidate, but must register by a set deadline and if unopposed, they must achieve at least the same number of votes as required on the original petitions.
In March 2012, I ran for Algonquin Township 45th Precinct Committeeman as a write-in candidate. My name was not on the ballot, but I was properly registered as a write-in candidate. I won that race with 20 write-in votes. I was unopposed. If I had only received 9 votes, I would have lost.