Cologne - While the Bundesliga's many stars continue to build up their fitness levels ahead of the new season, clubs up and down the country are working tirelessly behind the scenes to strengthen their playing staff in time for the big kick-off in mid August.

Over the next few weeks, bundesliga.com will be taking a closer look at each of the 18 top-flight clubs' summer transfer dealings so far. Next up in the series: TSG 1899 Hoffenheim.

How they fared in 2014/15

While Hoffenheim can justifiably be pleased with a season which brought improvement across the board, and in particular in the defence, there was disappointment at the WIRSOL Rhein Neckar Arena with an eighth-placed finish and the subsequent failure to qualify for Europe. Given that the side were seventh or higher virtually all season, the late collapse was particularly galling, yet it was the price to pay for an inconsistent Rückrunde in which the Sinsheimers were unable to win back-to-back games.

Ins...

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Mark Uth (r.) (SC Heerenveen)

  • Cologne-born 23-year-old centre-forward.
  • Registered 15 goals and 11 assists in the Eredivisie last season.

What he offers: Composure in front of goal, a powerful left foot and clever movement.

Fabian Schär (FC Basel 1893)

  • Right-footed centre-half, 23, who has 13 caps for Switzerland.
  • Made seven UEFA Champions League appearances in 2014/15.

What he offers: Composure in possession, a threat from set-pieces and excellent reading of the game.

Jonathan Schmid (SC Freiburg)

  • Versatile attacking midfielder, 25.
  • Picked up an impressive 11 assists for Freiburg last season, scoring four goals.

What he offers: Creativity, impressive work ethic and plenty of Bundesliga experience.

Outs...

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Roberto Firmino (r.) (Liverpool FC)

  • Attacking midfielder with ten Brazil caps to his name, 23.
  • Scored 38 goals in 140 Bundesliga appearances for Hoffenheim.

Andreas Beck (Besiktas JK)

  • Solid 28-year-old right-back who had been at TSG since 2008.
  • Veteran of 243 Bundesliga appearances, he won the title with VfB Stuttgart in 2007.

Anthony Modeste (1. FC Köln)

  • Powerful French striker, 27.
  • Scored 19 goals in 55 Bundesliga outings.

To-do list...

Markus Gisdol's (l.) squad looks powerful in most areas. Oliver Baumann will continue in goal, while the already impressive defence will be bolstered by the arrivals of young duo Pavel Kaderabek and Schär. Sebastian Rudy, Pirmin Schwegler and Eugen Polanski offer a wealth of experience in central midfield, while Uth is a more than capable replacement for Modeste up front. The one area of concern for the 45-year-old tactician is perhaps the attacking midfield, where, despite the signing of Schmid, the Sinsheimers will need to try and fill the creative void left by Firmino.

Editor's note: Not all summer transfers will be discussed here. The players featured in this article made at least ten league appearances for their respective clubs last season, chipped in with numerous goals and assists or made other significant contributions to their team. For an overview of the 2015/16 summer transfers, click here.