Please pay attention at the back, especially the fashion professionals (PRs and retailers, that means you) skulking out of earshot and confusing consumers by describing long evening dresses as "maxi dresses".

We went to great lengths (excuse the pun) last summer to explain the difference between a maxi dress and a long evening dress. So listen up, because we are recapping (there will be a test): as we pointed out back then, if the dress is made of chiffon, organza, lace, taffeta or any other traditional eveningwear fabric it is not a maxi; it's an evening dress with an identity crisis.

A maxi dress is a long version of a day dress, made from cotton, lawn, jersey or even silk, but it is not - and this is the crucial bit - a formal dress for eveningwear, so please stop calling a long evening dress a "maxi".

Okay, now we have cleared that up, let's get on to the subject of longer lengths this summer. You will have noticed that the maxi dress, which took roughly three years to make the transition from desirable, cutting edge catwalk garment by designers such as Zac Posen, Pucci, Cavalli and Diane von Furstenberg to 2010 high street ubiquity, is still highly visible for spring/summer 2011.

While the fashionistas have moved on to non-gypsy/non-hippie shapes and midis - of which more later - the maxi dress, with its early 70s hippie vibe works perfectly well for hot, high-summer days and poolside lunches. Worn with flat sandals or even roughed up with cage sandals, a floaty, flower-print maxi is a pretty, easy alternative to jeans. Find well-priced ones at Warehouse, H&M, Oasis and M&S.

If you want to do a city maxi, choose one in a plain fabric in a more architectural shape, like the scoop-neck, long-sleeve jersey maxi by Reiss; a drapey one with gently billowing shape by Complexgeometries from Browns; a sleeveless linen/cotton V-neck shirt dress in navy with gold buttons by Nicole Farhi, £380 at Fenwick, Bond Street, or a non-frilly floral print one by Topshop Limited Edition at £150.

The maxi skirt, the simple almost straight, to the floor baby, as pioneered by Raf Simons at Jil Sander is the uber-shape maxi skirt for summer, with the long pleated skirt waving its arms for recognition as a desirable alternative. Wear either shape with a plain white T-shirt and, when the temperature drops, a leather biker jacket or a boyfriend blazer. You can buy the original Jil Sander silk twill maxi skirt at Browns (£590), or find architecturally simple maxis at rock-bottom prices at Zara and H&M, or a fab silk version in coral at Reiss, or in navy silk by Theory at Fenwick, W1. A.L.C. has a long pleated maxi (£590) at Matches or there are unpressed pleats at H&M.

The totally new length for this season is - perhaps unsurprisingly with all things 70s hitting the shops everywhere from Browns and Matches to the high street - the midi.

Stella McCartney may be regarded as the Godmother of the midi, having produced a mid-calf, button-through denim skirt in her S/S 2010 collection which propelled "mum chic" - aka the midi - into the fashion limelight.

This newer, mid-calf length is turning up in skirts and dresses across the designer collections and is just beginning to creep into the high street. And while it looks fresh and rather charmingly wearable, it would be negligent of me not to point out the risk of "mum-chic" turning into plain old "mumsy" if you don't obey the style rules for midis. Rule 1: if you feel tempted by the midi there is no hiding place for legs. You need to work this length with bare legs - neither opaques nor, God forbid, clear tights are allowed, which means regular waxing and pedis until autumn. Rule 2: while ballerina flats are tempting, resist: you need something edgier. Cage sandals, open-toe boots and platform sandals all work with midis. Non-pretty, strappy, flat sandals can work if you really can't abide heels.

Find midis at Topshop, which has embraced the midi trend with A-line and button-through skirts, and at Zara which has a gorgeous mid-calf nude pleat skirt. Warehouse, H&M, Oasis and (please don't faint) Primark all have great midi dresses, including a very Marc Jacobs colour block baby at Primark.