Dublin is generally a very safe city during the day by American and European standards but can be an intimidating place on weekend nights. As in most other large cities, a few crimes against the person, such as muggings, unprovoked attacks, and robberies, have been known to occur in Dublin. Treat Dublin as you would other western cities, and be sensible: never walk in poorly-lit areas at night, especially alone; as Dublin centre is relatively compact, be aware that walking a few blocks can take you into some bad areas. Areas where crimes against foreigners have occurred include Rialto and western parts of the North Circular Road. Be especially vigilant or preferably avoid all together walking around the city centre after bar closing times on weekends (02:30-03:00) when very drunk people looking to take advantage of other drunk people roam the streets and when violent behaviour and crime are most likely to occur. Most homicides in the city are gang related.
Avoid the Boardwalk and Lower Abbey Street as a large number of drug addicts hang around these areas due to nearby drug rehabilitation centres.
You will, however, see a wide variety of buskers and street performers, these are normal people just plying their trade; they are usually very helpful for directions and appreciate your donations. (Busking and street performance is an old and vibrant part of Irish culture, and there is nothing unusual or unsavory about a person playing an instrument or performing in a public place even in the small hours of the morning. So approach and appreciate these talented and friendly individuals. Be aware that it is considered rude to photograph a street performer without tipping.)
If people approach you on the street, they could indeed be people just looking for directions, charity workers looking for donations, or people simply looking for a cigarette lighter. Be aware that Dublin people are usually open and unlike big cities like London or New York, talking to complete strangers is a common and regular occurrence.
If someone who appears to be drunk, under the influence of drugs or a habitual drug user, approaches you asking if they can talk to you for a moment, it is wise to keep walking (although expect drunk people to talk to you in a pub as it is common). These people may simply ask you for a cigarette or some money for a bus, but be aware that most Dubliners, even if they have no money, would never ask a stranger for money or cigarettes (although asking for a light for a cigarette is common). There are several scams being used on unaware tourists and locals alike so please be careful and use your judgement. If someone comes to you on the street, touches you, and asks you for something, say "no" or "sorry" and walk away. Again, locals will almost never behave like this so avoid people who do.
When driving, leave nothing valuable visible in your car, lock doors while driving through slow traffic in the city. There are plenty of taxis at all hours of the day and night, which are safe and usually friendly.
Never be afraid to approach Gardai (police officers) to ask for help or directions, It is their job to help. If you do get into trouble somehow and fear for your safety (which is very rare) and cannot find a Gardai officer, head to the nearest establishment such as a bar or shop where you will be safe. Call the emergency services on "999" or 112, free from any phone, and ask for the relevant service. If you have no phone, ask anyone working in a shop or bar to call the police for you, and the employee will gladly assist. Also, most doormen and bouncers in pubs will gladly call the police for you if you explain your situation.
Dublin has heavy traffic, and even if several of the locals tend to cross the road without having a green man, it is not recommended to follow this example. Hardly any of the cars slow down in front of zebra-crossings in busy and crowded streets.
If you rent a bicycle, ensure you rent full safety wear (helmet and lights) failure to do so can (albeit it rarely) result in fines. If possible, travel by foot or public transport is best.
Care should also be used when taking some of the "Nitelink" buses that frequent the city as they, while often safe, have seen their fair share of trouble. Sit downstairs if possible, if only to avoid the more raucous singing, shouting, and post-drinking vomiting.
Taxis are well regulated in Ireland, but many taxi drivers have been known to take longer routes when tourists are being carried, ask for the quickest route. If staying in a hotel or hostel your host may be able to help you acquire a reputable taxi.
The area around Temple Bar is both an attraction for tourists and for pickpockets. Be aware of your surroundings.
Be aware when crossing over roads where pedestrians have an official right of way sign, as these are frequently ignored by Dublin motorists particularly taxis, also beware than unlike a lot of European cities, Dublin cyclists will nonchalantly cycle on footpaths. This often happens even when there is also a cycle lane right beside the path, something that, in turn, is frequently ignored by the Gardai.
Most suburbs on all sides of the city are very safe, but there are a few rough areas, mostly on the Northern and Western peripheries of the city, which are seldom visited by tourists but might warrant some caution. Nonetheless, those interested in urban regeneration may find a visit to Ballymun (home to Ireland's most well known tower-blocks as well as Swedish furniture superstore IKEA) and Tallaght (a historic village that was developed into a 70,000-strong residential suburb) of interest.