故意犯罪往往會經過一個較長的過程，在這當中可劃分幾個階段來加以觀察，即從開始「產生犯罪動機」，「形成犯罪決定」，「經過準備犯罪」，「著手實行犯罪」、一直到「完成犯罪」或「結果發生」。不過並不是所有的故意犯罪都會經過這樣一個過程。有些故意犯罪，它可能進行到某一個階段便停頓下來而沒有再進行下去。這裡乃涉及到一個刑法上的重要問題：故意犯罪
各種可能的行為發展階段或形態，刑法究竟要不要處罰以及應該如何處罰。相反的，過失犯罪，一般認為並沒有所謂行為階段的問題。是以，本文所探討的便是專門針對故意犯罪而論，同時依照通常的發展階段及台灣與中國兩岸的刑法規定，區分「犯意形成或犯意表示」、「（犯罪）
預備」、「著手實行」、「不能未遂」、「中止未遂」、「犯罪完成」階段，分別加以論述比較。

Intentional crime often go through a longer process, which can be observed from a number of stages as follows: "produce criminal motive",
"form criminal decision", "prepare to commit crime", "attempt to realize",
"finish" or "result". But not all intentional crimes necessarily go through this process. For example, some come to a halt at a certain stage and do not proceed to the final. We came across an important problem related to the criminal law: regarding to stages of possible behavioral developments or forms in intentional crime, should the lawbreaker be punished by criminal law, or how? On the other hand, involuntary crime is generally considered to have no such behavior stage problems.As a result, this study attempted to focus upon intentional crime. In the meanwhile, it discussed general development stages and criminal law regulations
in Taiwan and mainland China over the following stages: "forming or
expression of mens rea", "(crime) preparation", "attempt to realize", "disabled attempt", "retirement of attempt", and "completion".