The definitions for attempt crimes vary from state to state, but generally, attempted offenses occur when an individual has an actual intent to commit a crime (in legal terms, specific intent), and takes direct action towards completion of the crime. Typically, an individual will have failed to complete the crime, but this is not necessarily required. One common example of an attempted crime would be attempted murder, where an individual must have the intent to kill another individual, then take action towards that end but fall short of actually doing so.
Because, by their vary nature, attempt crimes are typically incomplete, establishing the intent of an individual is often the key to securing a conviction. Thus, in the example above, it is important to note that it would not be enough for an individual to intend only harm or even serious harm to a victim, for purposes of an attempted murder conviction.
In some jurisdictions, the actions or acts taken for an attempted crime must go beyond "mere preparation" for the offense. However, other jurisdictions permit a conviction based on a wider range of actions taken towards completing a crime.