A　series　of　polyoxometalates　(POMs)　that　incorporate　the　highest-nuclearity　Ln　clusters　that　have　been　observed　in　such　structures　to　date　(Ln26,　Ln=La　and　Ce)　are　described,　which　exhibit　giant　multishell　configurations　(Ln⊂W6⊂Ln26⊂W100).　Their　structures　are　remarkably　different　from　known　giant　POMs　that　feature　multiple　Ln　ions.　In　particular,　the　incorporated　Ln–O　clusters　with　a　nuclearity　of　26　are　significantly　larger　than　known　high-nuclearity　(≤10)　Ln–O　clusters　in　POM　chemistry.　Furthermore,　they　also　contain　the　largest　number　of　La　and　Ce　centers　for　any　POM　reported　to　date　and　represent　a　new　kind　of　rare　giant　POMs　with　more　than　100　W　atoms.　Interestingly,　the　La26-containing　POM　can　undergo　a　single-crystal　to　single-crystal　structural　transformation　in　the　presence　of　various　transition-metal　ions,　such　as　Cu2+,　Co2+,　and　Ni2+,　from　an　inorganic　molecular　nanocluster　into　an　inorganic–organic　hybrid　extended　framework　that　is　built　from　POM　building　blocks　with　even　higher-nuclearity　La28clusters　bridged　by　transition-metal　complexes.　©　2017　Wiley-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim