The Staten Island Yankees, an A ball affiliate of the big-league team.
Zev Steinhardt
WAG Does there have to be a ‘Reason’?
It is for the same reason that the Upper Peninsula is a part of Michigan!
Does the cream rise to the top when the cow goes uphill?
When I was a kid, we used to go to Pouch Boy Scout Camp on Staten Island. Before the bridge was built there was also a ferry from Brooklyn, which had excellent soft serve ice cream. 
Yeah, but better get a haircut first.*
Hippie. 
*This advice of course would best apply to attempts to infiltrate certain South Shore eateries. The North Shore is much more eclectic and diverse.
And by the way, no one has mentioned doing a tour of palatial estates of Mafiosi (present or former; S.I. was notable for being a bedroom borough for upper-level thugs). You can also visit the spot on Hylan Blvd. where Lucky Luciano was dumped after being “taken for a ride”. He lived.
No one has answered the OP yet. Billdo and **Exapno Mapcase ** have told you why SI is part of New York State, but they have not explained why it is part of New York City.
Before getting to the reasons, it should be stated that there was no pre-colonial legal tie between the two municipalities; it was a deliberate and intentional act by Andrew Haswell Green to include SI in the consolidation of 1898, an act that also added Brooklyn and Queens to the territory of NYC. (The area of today’s Bronx had joined earlier.) During the debate that surrounded the creation of “Greater New York” quite a few persons argued to exclude SI from the scheme. It was too far away and too rural, they said.
So, why did Green include it? Three primary reasons, it seems.
#1. Staten Islanders Wanted In. After encountering some resistance to the idea of consolidating the entire metropolitan region into NYC, Green, the force behind the consolidation movement, proposed a non-binding referendum to feel out popular sentiment. SI was included in the vote. They voted nearly 4 to 1 in favor of joining NYC – the highest pro-consolidation vote of any voting district. (I love to tell this to today’s sucession-happy SIers!) This result is not so surprising because less-developed areas – and SI was very rural in nature – craved the infrastructure improvements that Manhattan’s tax wealth could give them.
#2. Unity of the Port. In the late 1800s (and for centuries prior) the economy of the metropolitan region was driven by the trade conducted at the Port of New York. Green and his supporters in the business community saw that the port was being mismanaged by the area’s fragmented, competing waterfront municipalities. There were port facilities on SI, and Green, who preached comprehensive urban planning since the 1860s, wanted them to be part of his vision of a centrally controlled harbor.
#3. Collateral. In the 19th century, the NYS constitution capped the amount of money a municipality could borrow (by issuing bonds) based on its assets. (It’s worth noting that Brooklyn, an independent city at the time, was fiercely torn between its autonomy and the allure of the public improvements that would come with consolidation. It had borrowed to its legal limit and could not afford the improvements it desperately needed. The unlit, unpaved, muddy streets of Brooklyn had been a joke in the popular press for decades.) Taxable land is an asset. Green knew that massive public improvements – bridges, sewers, roads, water supplies, etc. – would need to be built if Greater New York became a reality, and the real estate of SI represented collateral.
Note: I’d like to acknowledge Prof. David C. Hammack, who is generally regarded as the leading expert on the consolidation of Greater New York, for pointing out reasons #2 & 3 to me during my research. (You’d be amazed how often this very question comes up.)
See, wha’d I tell you.
Wow. As I read the thread, I wondered what kanicbird’s post referred to. Lived in NYC since 1981, I never knew this.
Live and loin
Cartooniverse
To expand on some previous posts, New York used to be significantly larger than its current size. Even leaving aside the fact that NY’s western border at one time theoretically extended through uncolonized land all the way to the Pacific, New York encompassed what is now Vermont, Nantucket Island, Martha’s Vinyard, and even parts of Maine.
Which explains why the district that encompasses Staten Island (as well as some of Brooklyn) elects the only Republican Congressman from New York City – Vito Fossella.
“Infiltrate”? This is going to be interesting. I don’t wear long hair anymore, but I’m not about to shave my goatee.
You don’t say. Most outsiders think NJ is the East Coast epicenter of mob life, thanks to the Sopranos.