Picture the occasion a decade ago, when the web was in its infancy. An employee is called into his manager's office. "You know," says the boss, "this World Wide Web sounds very exciting. Could you print it out for me to look at?"

In the early 1990s this task might just have been possible, but it is totally unimaginable today - and not just because of the web's vast size. The mountains of paper spilling across the manager's desk would depend on which employee printed it out. What you see online depends on who you are.

According to Datamonitor analyst Evan Kirchheimer, the personalisation of websites is "an attempt to counter-balance the anonymity that typically characterises interactions between consumers and large businesses, especially over the internet".

Companies now realise that what the internet offers in efficiency, it lacks in personal service. By parodying the human touch, website operators hope to form closer relationships with their customers. "We want to make marketing as personal and effective as a salesperson," says Cliff Allen, chief executive of Coravue, a California-based content management systems company. "If you call or meet a salesman, he'll ask you a few questions, look around, rub his chin and then say 'I reckon I know what's perfect for you.' We do the same online."

In the same way that the best sales staff remember your name, the online relationship must of course begin with recognition. Whether through a cookie file on your computer, or by making you register and log in, most websites now want to know your identity.

"Welcome back, John!" says the homepage of your favourite portal, customised to display news on your choice of topics and the prices of shares in your portfolio.

Customisation is the most basic personalisation technique, putting the user in control. By allowing users to state their preferences, many websites, such as lastminute.com and Yahoo!, offer pages that contain content - and marketing - most likely to interest the user.

But data collection rarely stops at what customers freely disclose. "The success of getting personal is to be covert," says Ben Hayman, founder of content management solutions provider, Mediasurface. "No one likes a pushy new friend that demands we tell them all about us before they give us anything back.

"Think of every bit of content and every person in the connected world as being in a continual state of adaptive relationship building, and you have the scale of the true challenge."

Through non-intrusive methods, it is also possible to build up a comprehensive file of transactions and behaviour, logged each time you click on a link, buy a product, alter your preferences or request information. Most companies believe that few customers, who are used to store loyalty cards, will react against this implicit data collection.

"I don't think there will be much resistance," states Mr Kirchheimer. "If there is an increase in convenience and relevance for the user they are willing to pay by giving away a little privacy."

So, with data files bulging, next comes the chin-rubbing - complex mathematical analysis to identify patterns of behaviour and profile individuals. With this knowledge website owners, helped by software, can decide how to respond to its customers, altering what appears on your screen to optimise a user's interaction with the company website.

Amazon.com, perhaps the world's most famous personalised website, makes book recommendations based on what books are often bought together. Japanese IT and software retailer Sofmap analysed its database of 2m customers to build a recommendation engine for its online store - it claims that profits rose 300 per cent in the month following the engine's implementation compared to the previous year.

With the lure of impressive gro