Croatia midfielder Mateo Kovacic (left) joined Real Madrid from Italian side Inter Milan for $29.2 million in August 2015.
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Argentine striker Luciano Vietto made the switch to the capital from Villarreal, costing Atletico $18.7 million in June 2015.
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Real Madrid signed Brazilian right-back Danilo from Porto for $31.7 million in July 2015.
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Another Brazilian defender, Felipe Luis -- pictured center -- rejoined Atletico Madrid for $16.4 million in July 2015 after just one year at Chelsea.
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Goalkeeper Kiko Casilla, 28, returned to Real from Espanyol for $6.1 million in July 2015.
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Belgian winger Yannick Ferreira Carrasco moved to the Vicente Calderón from French club Monaco for $18.7 million in July 2015.
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Montenegro defender Stefan Savic cost Atlético $25.2 million in July 2015, when midfielder Mario Suarez moved in the other direction to Italian side Fiorentina.
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Real Madrid's key signing of the January 2015 transfer window was Martin Odegaard (pictured right with Cristiano Ronaldo). The Norwegian teenager had attracted the attention of the world's biggest clubs.
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Atletico brought prodigal son Fernando Torres back to Madrid on loan in January 2015, and the former Liverpool and AC Milan striker signed a permanent deal in August.