I will start this topic by making a list of the tiaras that are currently worn by the Princesses and Queens of the European Royal Families (reigning and non-reigning).
But later we will also be able to talk about missing tiaras, others that were sold, etc...
Belgium
The Art Deco Bandeau Tiara: ca. early 20th century;
https://c1.quickcachr.fotos.sapo.pt/...062_qbMK6.jpeg
The Brabant Laurel Wreath Tiara: Hennel & Sons, ca. 1912;
https://c3.quickcachr.fotos.sapo.pt/...063_jsiFz.jpeg
The Diamond and Pearl Bandeau Tiara: provenance unknown;
https://c6.quickcachr.fotos.sapo.pt/...070_KCW2K.jpeg
The Nine Provinces Tiara: Van Bever, ca. 1926;
https://c10.quickcachr.fotos.sapo.pt...069_hh7J1.jpeg
https://c9.quickcachr.fotos.sapo.pt/...558_Y2wgG.jpeg
The Princess Claire Wedding Tiara: provenance unknown;
https://c5.quickcachr.fotos.sapo.pt/...071_Mm00d.jpeg
The Spanish Wedding Gift Tiara: ca. 1960;
https://c4.quickcachr.fotos.sapo.pt/...074_BTQsD.jpeg
https://c7.quickcachr.fotos.sapo.pt/...073_VTwzr.jpeg
https://c3.quickcachr.fotos.sapo.pt/...072_7LSDU.jpeg
The Wolfers Tiara: Wolfers, ca. 1960;
https://c7.quickcachr.fotos.sapo.pt/...078_E4ohG.jpeg
https://c8.quickcachr.fotos.sapo.pt/...077_sOm8D.jpeg
The Savoy-Aosta Tiara;
https://c8.quickcachr.fotos.sapo.pt/...678_YIsOu.jpeg
Denmark
The Baden Palmette Tiara: Koch, ca. 1856;
https://c5.quickcachr.fotos.sapo.pt/...9084_zLYib.png
The Crown Princess Mary Wedding Tiara: provenance unknown;
https://c1.quickcachr.fotos.sapo.pt/...085_2yJ8u.jpeg
https://c7.quickcachr.fotos.sapo.pt/...086_eryho.jpeg
The Emerald Parure Tiara: C.M. Weisshaupt, ca. 1840;
https://c8.quickcachr.fotos.sapo.pt/...089_P94vb.jpeg
https://c4.quickcachr.fotos.sapo.pt/...090_TWzh5.jpeg
The Flora Danica Tiara: Flora Danica, ca. 2011;
https://c8.quickcachr.fotos.sapo.pt/...092_qHH4m.jpeg
The Floral Aigrette Tiara: ca. 19th century;
https://c1.quickcachr.fotos.sapo.pt/...094_AzEHZ.jpeg
The Golden Poppies Tiara: Arje Griegst, ca. 1976;
https://c5.quickcachr.fotos.sapo.pt/...096_mFkt7.jpeg
The Midnight Tiara: Charlotte Lynggaard, ca. 2009;
https://c1.quickcachr.fotos.sapo.pt/...097_RSz7M.jpeg
The Nassut Tiara: Nicolai Appel, ca. 2012;
https://c8.quickcachr.fotos.sapo.pt/...100_hDOQP.jpeg
The Pearl Poiré Tiara: ca. 1825;
https://c3.quickcachr.fotos.sapo.pt/...098_9ff9V.jpeg
https://c4.quickcachr.fotos.sapo.pt/...099_1zkYl.jpeg
The Ruby Parure Tiara: ca. 19th century;
https://c2.quickcachr.fotos.sapo.pt/...106_R2myz.jpeg
https://c3.quickcachr.fotos.sapo.pt/...107_BePMg.jpeg
The Princess Dagmar Floral Tiara: ca. early 20th century;
https://c7.quickcachr.fotos.sapo.pt/...109_20nCU.jpeg
The Princess Thyra Sapphire Tiara: ca. 19th century;
https://c7.quickcachr.fotos.sapo.pt/...110_C2y8i.jpeg
The Turquoise Daisy Bandeau Tiara: ca. 20th century;
https://c2.quickcachr.fotos.sapo.pt/...112_E10dl.jpeg
Spinel Necklace tiara;
https://c4.quickcachr.fotos.sapo.pt/...498_PBsl4.jpeg
https://c2.quickcachr.fotos.sapo.pt/...499_OoLv2.jpeg
Princess Benedikte’s Floral Tiara;
https://c8.quickcachr.fotos.sapo.pt/...501_ucvoZ.jpeg
Queen Sophia’s Star and Pearl Tiara;
https://c5.quickcachr.fotos.sapo.pt/...502_1a2zR.jpeg
https://c2.quickcachr.fotos.sapo.pt/...503_mk1d2.jpeg
Queen Alexandrine of Denmark's Diamond Drop Tiara;
https://c4.quickcachr.fotos.sapo.pt/...553_HFhtm.jpeg
Khedive of Egypt Tiara;
https://c7.quickcachr.fotos.sapo.pt/...504_RdK1O.jpeg
Liechtenstein
The Habsburg Fringe Tiara: Köchert, ca. 1890;
https://c5.quickcachr.fotos.sapo.pt/...137_KvIf2.jpeg
https://c3.quickcachr.fotos.sapo.pt/...136_rzWbj.jpeg
The Kinsky Honeysuckle Tiara: ca. 1870;
https://c8.quickcachr.fotos.sapo.pt/...138_5Rrc2.jpeg
Princess Margaretha's Sapphire Necklace Tiara;
https://c2.quickcachr.fotos.sapo.pt/...909_fwYIG.jpeg
Luxembourg
The Amethyst and Pearl Bandeau Tiara: provenance unknown;
https://c9.quickcachr.fotos.sapo.pt/...388_iBFiL.jpeg
The Aquamarine Bandeau Tiara: ca. 20th century;
https://c1.quickcachr.fotos.sapo.pt/...389_ezfgl.jpeg
The Belgian Scroll Tiara: Henry Coosemans, ca. 1953;
https://c10.quickcachr.fotos.sapo.pt...391_uDKwc.jpeg
The Chaumet Emerald Tiara: Chaumet, ca. 20th century;
https://c2.quickcachr.fotos.sapo.pt/...399_UZuvV.jpeg
The Citrine and Pearl Bandeau Tiara: provenance unknown;
https://c8.quickcachr.fotos.sapo.pt/...400_z1Bqk.jpeg
The Congo Diamond Necklace Tiara: Van Cleef & Arpels, ca. 1953; rarely worn
https://c4.quickcachr.fotos.sapo.pt/...9401_649hZ.png
The Emerald Peacock Necklace Tiara: Van Cleef & Arpels, ca. 1956;
https://c7.quickcachr.fotos.sapo.pt/...402_byBoy.jpeg
The Empire Tiara: ca. 19th century;
https://c4.quickcachr.fotos.sapo.pt/...404_6hLm3.jpeg
The Grand Duchess Marie-Adelaide Tiara: ca. 19th century;
https://c1.quickcachr.fotos.sapo.pt/...9409_wZ9S9.png
The Luxembourg Vine Tiara: ca. 19th century;
https://c4.quickcachr.fotos.sapo.pt/...412_4sZKp.jpeg
The Pearl and Diamond Choker Tiara: Chaumet;
https://c1.quickcachr.fotos.sapo.pt/...9414_2mJ5j.png
The Sapphire Art Deco Tiara: provenance unknown; rarely worn
https://c10.quickcachr.fotos.sapo.pt...415_HuZd0.jpeg
The Small Nassau Floral Tiara; provenance unknown;
https://c7.quickcachr.fotos.sapo.pt/...416_PTsQw.jpeg
The Turquoise Tiara: ca. 20th century;
https://c5.quickcachr.fotos.sapo.pt/...417_NnTPW.jpeg
The Weiller Art Deco Tiara: ca. 1990s;
https://c8.quickcachr.fotos.sapo.pt/...9419_rH5Bk.png
Queen Victoria Eugenia's Aquamarine Tiara;
https://c8.quickcachr.fotos.sapo.pt/...717_cT7Ur.jpeg
Monaco
The Bains de Mer Tiara: Cartier, ca. 1956; rarely worn
https://c1.quickcachr.fotos.sapo.pt/...9380_AJnwg.png
The Baumer Aigrette Tiara: Lorenz Bäumer, ca. 2011;
https://c3.quickcachr.fotos.sapo.pt/...381_ID6Oz.jpeg
The Cartier Pearl Drop Tiara: Cartier, ca. 1920;
https://c2.quickcachr.fotos.sapo.pt/...382_E0Cey.jpeg
The Grimaldi Sapphire Necklace Tiara: provenance unknown;
https://c4.quickcachr.fotos.sapo.pt/...383_L0hVK.jpeg
The Ocean Tiara: Van Cleef & Arpels, ca. 2011;
https://c5.quickcachr.fotos.sapo.pt/...384_Me7TH.jpeg
The Princess Charlotte Fringe Tiara: provenance unknown;
https://c5.quickcachr.fotos.sapo.pt/...385_zZyDV.jpeg
The Serre-Chignon Tiara: ca. 1956; rarely worn
https://c3.quickcachr.fotos.sapo.pt/...387_Q59WF.jpeg