Chelsea's business in the transfer market this summer has understandably drawn envious looks from rival clubs across Europe.

The Blues have brought in six new signings so far, with German starlet Kai Havertz the most expensive purchase at £72m.

Timo Werner (£47.7m), Hakim Ziyech (£36m), Ben Chilwell (£45.18m), Thiago Silva (Free transfer) and Malang Sarr (Free transfer) have also been added to Frank Lampard's squad.

It's a transfer window that has the potential to rank as one of the best ever from an English club and Chelsea will be expected to challenge for the Premier League title in 2020/21 as a result.

The business conducted by the Blues this summer also suggests they have finally learned their lesson from 2017/18.

Havertz in training

After winning the Premier League title in Antonio Conte's first season in 2016/17, the Blues decided to spend big, but it all went disastrously wrong.

We've detailed Chelsea's acquisitions from that fateful season below and it's no surprise that Conte's stint as manager of the club was short-lived.

Chelsea's 2017/18 transfers

Summer:

Alvaro Morata - £59.4m

Tiemoue Bakayoko - £36m

Danny Drinkwater - £34.11m

Antonio Rudiger - £31.5m

Davide Zappacosta - £22.5m

Zappacosta with Chelsea

Ethan Ampadu - £2.52m

Willy Caballero - Free transfer

January:

Emerson - £18m

Olivier Giroud - £15.3m

Ross Barkley - £15.12m

Barkley with Chelsea

Of the 10 players signed, only two can be labelled as 'successful'.

Rudiger has been a regular starter for the Blues since his arrival from AS Roma, although his place in the team is now under threat following the signing of Silva.

Then you have Giroud, who has been a consistent performer under Conte, Maurizio Sarri and Lampard since joining from London rivals Arsenal.

Ampadu is a player we will spare from criticism, as the Welsh international is in the very early stages of his career and does look a promising talent.

Ampadu with Chelsea

But the rest of the signings made by Chelsea during the 2017/18 season were nothing short of woeful.

Drinkwater will forever rank as one of the worst big-money signings in Premier League history, while Morata and Bakayoko are not far behind the Englishman in that respect.

Emerson is currently being kept out of the team by Marcos Alonso and Caballero hasn't even managed to oust the heavily criticised Kepa Arrizabalaga from the starting XI on a regular basis.

The less said about Barkley's time at Chelsea, the better. Surely the 2020/21 transfer window can't turn out like 2017/18, can it?