One of the things about being an independently-working, rather than transferred-and-sponsored, expat in Hong Kong, is that you start to get a bit into the visa laws. I've had a change of legal status 5 times since I got to HK, and I'm hoping for a different - and more interesting - one soon. Almost all expats will come under one of 4 possible visas:

Visitor

The simplest status, given to most (Western) entrants when we arrive in Hong Kong. This status allows you to stay in Hong Kong for a fixed period (6 months for Brits, 3 months for most other Westerners), and allows you to do business, but does not allow you to work in Hong Kong. Technically, even volunteer work is forbidden, although I'm not sure how well-enforced that is. Leaving Hong Kong - either for a genuine trip, or a visa run to Macau or Shenzhen - and returning will get you a new stamp and reset your countdown, but you can't do it indefinitely, since sooner or later Hong Kong Immigration will decide you are actually living here and will, so I'm told, first issue a short visa (e.g. 1 month) and then formally warn you that it will not be renewed. They are pretty flexible though - after my first Employment Visa ran out in October 2006, I was given enough stamps to stay in Hong Kong until at least December 2007 simply by living my life here, with no 'artificial' visa runs. Many expats enter HK on a visitor visa, later converting it to a...

Employment Visa

I would guess that most expats in HK have Employment Visas, which allow them to work in a specified job for a specified period of time. In theory, if you lose your job, you also lose your visa, but in practice you're allowed to stick around until your visa runs out, partly in the expectation that you'll either get a new job (and apply for a new visa) or leave HK in that time. The first issued visa is normally 1 year, with renewals being for 2-3 years. Renewals are pretty much a rubber-stamp as long as the visa holder is still in the same job. Applications are not too complicated, needing a CV with proof (references, educational certificates, etc.) from the applicant, and business information from the company. The biggest companies in Hong Kong, who employ a lot of expats, can breeze through an application.

Dependent's Visa

This has come and gone over the past few years, but as of now, the situation is pretty simple. If you are granted a Hong Kong visa (e.g. employment visa), your spouse may apply for, effectively, the same rights you have - so if you have the right to work in Hong Kong, your spouse may apply for the same. As long as you have an established relationship (i.e. it's not a quickie marriage to get a visa) and your spouse is 'clean' (no criminal record, etc.) I think it's normally a rubber-stamp. These rights have changed a couple of times, but are generally accepted as a way of encouraging (appropriate) immigration, by making it easier for immigrants to bring their families.

Permanent Resident

After 7 years of continuous residence in Hong Kong, a temporary resident can apply for permanent residency, which allows for indefinite stay, employment and other rights, without having to explicitly apply for them. I think the documentation requirements are quite strict for this, in terms of proving your residency, and it can take a few months to be processed, but once it's done, you are effectively no longer an immigrant. One slight kicker, which has bitten me already, is the 7 years continuous requirement - since I have had periods of visitor status between my employment visas, I currently have 0 time I can put towards the 7 years. Similarly, I believe that you have to have been physically present in Hong Kong for at least 6 months of each of the 7 years, or you are not counted as resident for that year.

In the meantime, I've applied for entry under the Quality Migrant Admission Scheme which - if my application succeeds - will allow me to stay and work in Hong Kong without needing an explicit employment visa for any work I do. More details to follow...

None of this constitutes formal advice, etc. etc. - it's just my understanding of the situation having lived here for a few years and been though a couple of different visa processes.