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 are the Billy-Goats, 1. FC Köln…

How they fared in 2014/15...

You won't hear the Köln fans complaining after the Billy Goats comfortably negotiated their first season back in Germany's top flight after winning the Bundesliga 2 title in 2013/14. A solid defensive foundation ensured they became the only promoted side to go an entire season without spending a single day in the relegation zone: to reinforce the point, only the top four - FC Bayern, VfL Wolfsburg, Borussia Mönchengladbach and Bayer 04 Leverkusen - conceded fewer goals all campaign.

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Ins...

Outs...

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.