!!! Please read this info: Croatia has signed an accession treaty to become the 28th member of the European Union in July 2013, following six years of negotiations with the regional bloc.
http://www.aljazeera.com/news/europe/2011/12/201112104312922332.html

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Who requires a visa?
Croatia is not a member of the European Union but UK citizens (including children under 16) and citizens from other EU countries need only a valid passport. Holders of non-EU passports should check with the appropriate consulate to see if a visa is required.

The following categories of aliens do not require a visa for entering the Republic of Croatia:
1. Holders of valid Schengen residence permits;
2. Holders of valid Schengen visas arriving on cruise ships sailing out of a port in one of the Schengen states;

Other nationals require a Visa to enter Croatia.

How long is the visa valid for?
TRAVEL VISA
Travel visa may be issued for one, two or multiple entries into the Republic of Croatia, for tourist, business, personal or other purposes.

TRANSIT VISA
Transit visa may be issued one, two or exceptionally several transits through the territory of the Republic of Croatia, with a validity period of up to 6 months. On the basis of a transit visa, an alien may stay in the Republic of Croatia for a period of up to 5 days upon each journey. Transit visa may be issued to an alien if he/she has secured entry into the state to which he/she is traveling.

AIRPORT TRANSIT VISA
As a general rule, an alien who shall not leave the international transit area in between flights at a Croatian airport or on international flights shall not require a visa. By way of derogation from that rule, the Croatian Government may stipulate that nationals of certain countries and holders of travel document issued by authorities of such countries shall require an airport-transit visa.

VISA IN A COMMON TRAVEL DOCUMENT
This is a transit visa for a single transit, or a travel visa limited to a maximum of thirty days, which may be issued to a group of between 5 and 50 people, in a common travel document, provided that the members of the group enter the territory of the Republic of Croatia, stay there and leave it as a group. The leader of the group shall possess an individual passport in which, where necessary, an individual visa is affixed.

- Validity period of a travel visa is up to one year. Continuous stay or total duration of consecutive stays may not exceed 90 days in the period of 6 months, counting from the date of first entry.
- On the basis of a transit visa, an alien may stay in the Republic of Croatia for a period of up to 5 days upon each journey with a validity period up to 6 months.
- An airport transit visa is issued for one, two or several transits through the airport international transit area, with validity period of up to 3 months.

Other information:
What is the cost of a Visa?
Airport-transit Visa 36 EUR (51 USD);
Transit Visa 36 EUR, (51 USD);
Travel Visa 36 EUR, (51 USD);
Travel or Transit Visa in a common travel document 36 EUR + 1 EUR per person (51 USD + 1 USD per person);
In case of urgent issuance of visa when the application has been submitted, without justification, three or less days prior to the intended journey 71 EUR (103 USD).

Following categories of persons are exempted from visa application fees:
- Members of immediate family of a Croatian national (spouse and children),
- Children under the age of six,
- Holders of diplomatic and official passports traveling officially.