This paper aims to examine the diachronic development of gerunds and analyze their internal structure and grammatical function. In OE and Early ME nominal gerunds behaved like nouns describing actions. From Late ME and onwards nominal gerunds began to acquire verbal properties. A verbal gerund in Present-Day English is composed of mixed projections [＋N,＋V]. The [＋N]-feature denoting nominal properties is related to licensing a gerund's logical subject. The [＋V]-feature denoting verbal properties is connected with licensing its verbal complement. So, it is necessary to stipulate a functional category Gerund Phrase in the internal projection of gerunds. Thus, the head Ger of the Gerund Phrase makes it possible to combine nominal and verbal features within the 'V＋ing'. The Ger bears the uninterpretable verbal feature [＋V] that is checked against the interpretable feature [V] of the verbal complement. It also bears the interpretable nominal feature [＋N] that functions as a nominalizer and guarantees a gerund's logical subject. As for the Case identification of a gerund's logical subject, it is spelled out as a genitive at the DP level when it is selected as the genitive form morphologically. But it is spelled out as an accusative when EPP attracts a nominal element as a clausal gerund's logical subject onto the FinP-TPdef level where the [FinP－finiteness] renders default Case feature to be accusative.