PE sponsors seeking new ways to increase margins and attract investors may wonder about the viability of using series entities – e.g., series limited liability companies (Series LLCs) – to decrease costs and increase operational efficiencies. Although their use in the PE space has been relatively limited so far compared to in the mutual fund industry, a fresh look at those structures may be warranted in light of the introduction of Delaware registered series entities in 2019 and the customization options they can provide. This first article in a two-part series explores the different types of series entities; their use by PE sponsors (e.g., for pledge funds); the enormous flexibility they offer; and practical considerations when forming and operating them. The second article will delve into reasons why Series LLCs and related entities are not more widely used in the PE context, including debunking widely held misconceptions about how the vehicles save costs and ease administrative burdens for sponsors. See our three-part guide to pledge funds: “High Upside Fee Structure and Other Incentives for Adoption” (Apr. 9, 2019); “Key Investment Management Agreement Provisions” (Apr. 16, 2019); and “Deal Uncertainty Issues and Three Investment Vehicle Structures” (Apr. 23, 2019).