Here are some key storylines to keep an eye on as the convention begins.
Security around the Republican National Convention has been an area of concern for law enforcement officials for weeks, and recent domestic and international events have heightened those concerns.
Thousands of law enforcement officers were ordered to Ohio even before the fatal shootings of police officers in Baton Rouge, Louisiana. After yet another tragedy, the head of Cleveland's largest police union called for an emergency action to be taken to suspend the state's open carry laws during the convention.
Still, Cleveland Police Chief Calvin Williams stressed officers are "prepared for anything and everything" that could happen.
Donald Trump's campaign chairman, Paul Manafort, confirmed that Melania Trump will address the convention on the first night of the event.
Sources tell ABC that she spent the weekend preparing for the address in New Jersey.
The campaign has released no information about her speech's focus or its length, but those sources did not rule out the prospect of her husband's making an earlier-than-normal appearance at the convention in order to introduce his wife.
Who Else Will Be Taking the Stage
"Duck Dynasty" star Willie Robertson and actors Scott Baio and Antonio Sabato Jr. are slated to speak on behalf of the reality star turned presumptive Republican nominee.
It's Really the Second Week of Work for Republicans
Last-ditch efforts from Donald Trump opponents to let delegates vote for whomever they choose — which could have allowed for scuttling Trump's nomination — failed during those meetings, and the movement's leader told ABC News she would not attempt to force a vote at the convention.
Some efforts continue even as the convention gets underway. Anti-Trump delegates are hoping to block the entire rules package and persuade their colleagues to go rogue, encouraging them not to stick to their binding votes and to force recounts in their state delegations.
The Delegates Decide Their Rules and Platforms
The biggest assignment that delegates have today is voting on their party's platform and the rules of the convention, both of which were lined up in the rules committee meetings.
The GOP took hard positions on same-sex marriage and transgender restroom use, and establishment Republicans fended off attempts to strip power from the Republican National Committee and make the rules friendlier to conservatives.
ABC News' Ryan Struyk contributed to this story.