In this paper, the meaning and processing of the German conditional connectives (CCs) such as "wenn" 'if' and "nur wenn" 'only if' are investigated. In Experiment 1, participants read short scenarios containing a conditional sentence (i.e., If P, Q.) with "wenn"/"nur wenn" 'if/only if' and a confirmed or negated antecedent (i.e., P/not-P), and subsequently completed the final sentence about Q (with or without negation). In Experiment 2, participants rated the truth or falsity of the consequent Q after reading a conditional sentence with "wenn" or "nur wenn" and a confirmed or negated antecedent (i.e., If P, Q. P/not-P. // Therefore, Q?). Both experiments showed that neither "wenn" nor "nur wenn" were interpreted as biconditional CCs. Modus Ponens (If P, Q. P. // Therefore, Q) was validated for wenn, whereas it was not validated in the case of "nur wenn." While Denial of the Antecedent (If P, Q. not-P. // Therefore, not-Q.) was validated in the case of "nur wenn," it was not validated for "wenn." The same method was used to test "wenn" vs. "unter der Bedingung," "dass" 'on condition that' in Experiment 3, and "wenn" vs. "vorausgesetzt," "dass" 'provided that' in Experiment 4. Experiment 5, using Affirmation of the Consequent (If P, Q. Q. // Therefore, P.) to test "wenn" vs. "nur wenn" replicated the results of Experiment 2. Taken together, the results show that in German, "unter der Bedingung," "dass" is the most likely candidate of biconditional CCs whereas all others are not biconditional. The findings, in particular of "nur wenn" not being semantically biconditional, are discussed based on available formal analyses of conditionals.