While SharePoint lists can contain up to 30 million items, lists with more than 20,000 items require special handling to avoid performance issues. Predictive indexing can help optimize large lists by automatically creating indexes for common queries. When lists grow too large, options include moving items to folders with fewer than 5,000 items each, using metadata navigation to return subsets of results, or employing third party tools. Proper planning is key to successfully managing large SharePoint lists.