Halacha

הלכה א
הַהֶפְקֵר כָּל הַמַּחֲזִיק בּוֹ זָכָה. וְכֵן הַמִּדְבָּרוֹת וְהַנְּהָרוֹת וְהַנְּחָלִים כָּל שֶׁבָּהֶן הֶפְקֵר וְכָל הַקּוֹדֵם בָּהֶן זָכָה. כְּגוֹן הָעֲשָׂבִים וְהָעֵצִים וְהַפֵּרוֹת שֶׁל אִילָנוֹת שֶׁל יַעַר וְכַיּוֹצֵא בָּהֶן:
כסף משנה
1.
Whoever takes hold of ownerless property acquires it. Any objects found naturally in deserts, rivers and streams - e.g., grass, trees, wild fruit and the like - are ownerless. Whoever first takes hold of such an object acquires it.

הלכה ב
הַצָּד דָּגִים מִן הַיָּמִים וּמִן הַנְּהָרוֹת. אוֹ שֶׁצָּד עוֹפוֹת אוֹ מִינֵי חַיּוֹת. הוֹאִיל וְאֵין לָהֶם בְּעָלִים זָכָה. וּבִלְבַד שֶׁלֹּא יָצוּד בִּשְׂדֵה חֲבֵרוֹ. וְאִם צָד שָׁם קָנָה. וְאִם הָיוּ הַדָּגִים בַּבֵּיבָרִים שֶׁל בְּעָלִים וְכֵן חַיָּה וְעוֹף שֶׁבַּבֵּיבָרִים. אַף עַל פִּי שֶׁהוּא בֵּיבָר גָּדוֹל וְהוּא מְחֻסַּר צִידָה הֲרֵי זֶה שֶׁל בַּעַל הַבֵּיבָרִים וְהַצָּד מִשָּׁם הֲרֵי זֶה גַּזְלָן:
כסף משנה
2.
When a person catches fish in a sea or in a river, and similarly, when he catches fowl, or various wild beasts, since they are ownerless, he acquires them. He may not, however, hunt in a field belonging to a colleague. Nevertheless, if he snares an animal there, he acquires it.
If fish - or wild beasts or fowl - are in vivariums belonging to another person, they belong to the owner of the vivarium. A person who snares an animal there is considered to be a robber. This applies even if the vivarium is large and effort is required to snare the animal.

הלכה ג
אֲבָל הַלּוֹקֵחַ דָּגִים מִתּוֹךְ מְצוּדָתוֹ שֶׁל חֲבֵרוֹ כְּשֶׁהוּא בְּתוֹךְ הַיָּם. אוֹ שֶׁלָּקַח חַיָּה מִמְּצוּדָתוֹ כְּשֶׁהִיא פְּרוּסָה בַּמִּדְבָּר הֲרֵי זֶה אָסוּר מִדִּבְרֵי סוֹפְרִים. וְאִם הָיָה הַמְּצוּדָה כְּלִי וְלָקַח מִתּוֹךְ הַמְּצוּדָה הֲרֵי זֶה גַּזְלָן:
כסף משנה
3.
However, when a person takes a fish from the net of a colleague at sea, or takes a beast from a snare of a colleague set in the desert, this is prohibited by virtue of Rabbinic decree. If the snare could be considered to be a container, and the person took the fish or the animal from the container, he is considered to be a robber.

הלכה ד
הַפּוֹרֵס מְצוּדָה בִּשְׂדֵה חֲבֵרוֹ וְצָד בָּהּ חַיָּה אוֹ עוֹף אַף עַל פִּי שֶׁאֵין לוֹ רְשׁוּת לַעֲשׂוֹת דָּבָר זֶה קָנָה. וְאִם הָיָה עוֹמֵד בַּעַל הַשָּׂדֶה בְּתוֹךְ שָׂדֵהוּ וְאָמַר זָכְתָה לִי שָׂדִי קָנָה בַּעַל הַשָּׂדֶה. וְאֵין לְבַעַל הַמְּצוּדָה כְּלוּם:
כסף משנה
4.
When a person spreads out a snare in a field belonging to a colleague, and traps a beast or a fowl, he acquires it, even though he does not have permission to do this. If the owner of the field was standing in the field at the time the animal was trapped, and said: "My field acquires this on my behalf," the owner of the field acquires it, and the owner of the snare does not acquire anything.

הלכה ה
דָּגִים שֶׁקָּפְצוּ לְתוֹךְ הַסְּפִינָה קָנָה בַּעַל הַסְּפִינָה. שֶׁזּוֹ כְּחָצֵר הַמִּשְׁתַּמֶּרֶת הִיא וְאֵינָהּ חָצֵר הַמְהַלֶּכֶת. שֶׁהַמַּיִם הֵן שֶׁמּוֹלִיכִין אוֹתָהּ וְאֵינָהּ הוֹלֶכֶת מֵחֲמַת עַצְמָהּ:
כסף משנה
5.
When fish jump into a boat, they become acquired by the owner of the boat, for the boat is considered to be a protected courtyard. It is not considered to be a moving courtyard, because the boat does not move on its own. It is the water that moves it.

הלכה ו
גֵּר שֶׁמֵּת וְלֹא הוֹלִיד יִשְׂרָאֵל אַחַר שֶׁנִּתְגַּיֵּר אֵין לוֹ יוֹרְשִׁין אֶלָּא כָּל הַקּוֹדֵם וְהֶחֱזִיק בִּנְכָסָיו זָכָה. וְאֵין בַּעַל הַמֵּצַר יָכוֹל לְסַלְּקוֹ בְּדָמִים שֶׁזּוֹ כְּמַתָּנָה הִיא:
כסף משנה
6.
When a convert dies without having fathered a Jew after his conversion, he has no heirs. Instead, the first person who takes hold of his property acquires it. A neighbor does not have the right to buy the property from the person who took hold of it, because this is considered to be a gift.

הלכה ז
שְׁתֵּי שָׂדוֹת בְּנִכְסֵי הַגֵּר וּמֵצַר אֶחָד בֵּינֵיהֶן. הֶחֱזִיק בְּאַחַת מֵהֶן לִקְנוֹתָהּ קְנָאָהּ. הֶחֱזִיק בָּהּ לִקְנוֹת אוֹתָהּ וְאֶת חֲבֶרְתָּהּ. זוֹ שֶׁהֶחְזִיק בָּהּ קָנָה אֲבָל חֲבֶרְתָּהּ לֹא קָנָה. הֶחֱזִיק בָּהּ כְּדֵי לִקְנוֹת אֶת חֲבֶרְתָּהּ לֹא קָנָה אַחַת מֵהֶן. חֲבֶרְתָּהּ מִפְּנֵי שֶׁלֹּא הֶחֱזִיק בָּהּ. וְאוֹתָהּ מִפְּנֵי שֶׁלֹּא הֶחֱזִיק בָּהּ כְּדֵי לִקְנוֹתָהּ. הֶחֱזִיק בָּהּ כְּדֵי לִקְנוֹתָהּ וְלִקְנוֹת אֶת חֲבֶרְתָּהּ וְאֶת הַמֵּצַר שֶׁבֵּינֵיהֶן. אוֹ שֶׁהֶחְזִיק בַּמֵּצַר לִקְנוֹת שְׁתֵּיהֶן הֲרֵי זֶה סָפֵק. וְאִם בָּא אֶחָד וְהֶחֱזִיק בָּהּ כְּדֵי לִקְנוֹתָהּ זָכָה הָאַחֲרוֹן:
כסף משנה
7.
The following laws apply when there are two fields in an estate that belong to a convert, with one boundary marker between them. If a person manifests ownership over one of the fields with the intent of acquiring it, he acquires it. If he manifests ownership over it with the intent of acquiring both it and the other field, he acquires the field over which he manifested ownership, but he does not acquire the other field.
If he manifests ownership over one field with the intent of acquiring only the other field, he does not acquire either of them. He does not acquire the field over which he did not manifest ownership because he did not manifest ownership over it. He does not acquire the field over which he did manifest ownership because he did not manifest ownership with the intent of acquiring it.
If he manifests ownership over one field with the intent of acquiring it, the other field and the boundary marker between them, or if he manifests ownership over the boundary marker with the intent of acquiring both fields, there is an unresolved doubt with regard to the matter. If another person comes and manifests ownership over one of the fields itself with the intent of acquiring it, the latter person becomes the legal owner.

הלכה ח
וְכֵן שְׁנֵי בָּתִּים זֶה לְפָנִים מִזֶּה שֶׁהֶחְזִיק בְּאֶחָד מֵהֶן לִקְנוֹתוֹ וְלִקְנוֹת אֶת הַשֵּׁנִי לֹא קָנָה אֶלָּא זֶה שֶׁהֶחְזִיק בּוֹ בִּלְבַד. הֶחֱזִיק בְּאֶחָד מֵהֶן כְּדֵי לִקְנוֹת אֶת הַשֵּׁנִי אַף זֶה שֶׁהֶחְזִיק בּוֹ לֹא קָנָה:
כסף משנה
8.
Similarly, when two houses are located one within the other, if a person manifests ownership over one of the houses with the intent of acquiring both it and the other house, he acquires only the house over which he manifested ownership. If he manifests ownership over one house with the intent of acquiring only the other one, he does not acquire even the house over which he did manifest ownership.

הלכה ט
הַמַּחֲזִיק בִּשְׁטָר מִנִּכְסֵי הַגֵּר כְּדֵי לִקְנוֹת אֶת הַקַּרְקַע הַכְּתוּבָה בְּאוֹתוֹ שְׁטָר לֹא קָנָה אֶלָּא הַשְּׁטָר בִּלְבַד לָצוּר עַל פִּי צְלוֹחִיתוֹ וְכַיּוֹצֵא בָּזֶה:
כסף משנה
9.
When a person takes hold over a deed of sale within the estate of a convert with the intent of acquiring the land mentioned in that deed, he acquires only the document itself. He may use it to wrap around the top of a bottle or the like.

הלכה י
שָׂדֶה הַמְצֻיֶּנֶת בִּמְצָרֶיהָ כֵּיוָן שֶׁהִכִּישׁ בָּהּ מַכּוֹשׁ אֶחָד קָנָה אֶת כֻּלָּהּ. וְאִם אֵינָהּ מְצֻיֶּנֶת בִּמְצָרֶיהָ קוֹנֶה מִמֶּנָּה בְּאוֹתוֹ מַכּוֹשׁ כְּדֵי שֶׁיֵּלֵךְ הַצֶּמֶד בִּשְׁעַת חֲרִישָׁה וְיַחְזֹר. הַמֵּצַר וְהֶחָצָב שֶׁמְּתַחֲמִין בּוֹ תְּחוּמִין מַפְסִיקִין בְּנִכְסֵי הַגֵּר. וְכָל הַמַּחֲזִיק בְּשָׂדֶה לֹא קָנָה אֶלָּא עַד הַמֵּצַר אוֹ עַד הֶחָצָב:
כסף משנה
10.
When the boundaries of a field belonging to a deceased convert are clearly marked, when a person plunges a spade into the field in one place, he acquires the entire field. If the boundaries of the field are not clearly marked, by plunging the spade into that one place, he acquires only a portion over which a team of oxen will pass when plowing, before the team returns.
A boundary marker and a chatzav used to designate boundaries serve as cut-off points with regard to the estate of a convert. Whoever manifests ownership over the field acquires only up to the boundary marker or the chatzav.

הלכה יא
כָּל הַמַּפְסִיק לְפֵאָה מַפְסִיק בְּנִכְסֵי הַגֵּר. כֵּיצַד. הָיָה שָׁם נַחַל אוֹ אַמַּת הַמַּיִם וְכַיּוֹצֵא בָּהֶן לֹא קָנָה אֶלָּא עַד הַנַּחַל אוֹ עַד הָאַמָּה. וְכָל הַמַּפְסִיק בִּרְשׁוּת שַׁבָּת מַפְסִיק בְּנִכְסֵי הַגֵּר כְּגוֹן שֶׁהָיָה בֵּין שְׁתֵּי הַשָּׂדוֹת רְשׁוּת הַיָּחִיד אוֹ כַּרְמְלִית אֲפִלּוּ הָיָה בֵּינֵיהֶם רְשׁוּת שֶׁחוֹלֶקֶת לְגִטִּין:
כסף משנה
11.
Whatever is considered significant to create a separation with regard to the distribution of pe'ah is also considered significant to create a separation with regard to the acquisition of the property of a deceased convert.
What is implied? If there was a stream, an irrigation ditch or the like, the person seeking to acquire the field acquires only up to the stream or up to the irrigation ditch.
Whatever creates a distinction with regard to the domains of the Sabbath, creates a distinction with regard to the acquisition of the property of a deceased convert - for example, a situation where a private domain or a carmelit is interposed between two fields. Indeed, a distinction is created, even if the two fields were separated by a domain that is considered a distinction with regard to the transfer of a bill of divorce.

הלכה יב
כָּל דָּבָר הַמַּפְסִיק לְטֻמְאָה מַפְסִיק בְּנִכְסֵי הַגֵּר. כֵּיצַד. כְּגוֹן שֶׁנִּכְנַס אָדָם לְבִקְעָה זוֹ וְטֻמְאָה בַּבִּקְעָה בְּצִדָּהּ אַחֶרֶת וְאֵינוֹ יוֹדֵעַ אִם הִגִּיעַ לִמְקוֹם הַטֻּמְאָה אִם לָאו. כָּל מָקוֹם שֶׁמַּחֲזִיקִין אוֹתוֹ לְטֻמְאָה הֲרֵי הוּא כְּמָקוֹם אַחֵר, מֻחְלָק בִּפְנֵי עַצְמוֹ:
כסף משנה
12.
Whenever a distinction is created with regard to the laws of ritual impurity, it also applies with regard to the acquisition of the property of a deceased convert.
What is implied? A person enters a valley. There is an object that conveys ritual impurity on one side of the valley, and the person does not know whether or not he has reached the place that is ritually impure. Wherever the person would be considered to be ritually impure is considered to be a separate entity from the field as a whole.

הלכה יג
בִּקְעָה גְּדוֹלָה שֶׁיֵּשׁ בָּהּ שָׂדוֹת רַבּוֹת וְכֻלָּן שֶׁל גֵּר אֶחָד וְלֹא הָיָה בֵּינֵיהֶן לֹא מֵצַר וְלֹא חָצָב וְלֹא דָּבָר מִדְּבָרִים הַמַּפְסִיקִין. וּבָא אֶחָד וְהֶחֱזִיק בְּמִקְצָת הַבִּקְעָה לִקְנוֹת אֶת כֻּלָּהּ. כָּל הַנִּקְרָא עַל שֵׁם אוֹתוֹ הַגֵּר קוֹנֶה אוֹתוֹ:
כסף משנה
13.
The following law applies when there is a large valley containing many fields, all belonging to one convert, and there is no boundary marker, chatzav or any other entity that creates a distinction between them. If one person comes and manifests ownership over a portion of the valley with the intent of acquiring the entire valley, he acquires all the land that is known to be owned by that convert.

הלכה יד
עַכּוּ''ם שֶׁמָּכַר מִטַּלְטְלִין לְיִשְׂרָאֵל אוֹ קָנָה מִטַּלְטְלִין מִיִּשְׂרָאֵל. קוֹנֶה בִּמְשִׁיכָה וּמַקְנֶה בִּמְשִׁיכָה אוֹ בְּדָמִים. אֲבָל הַקַּרְקַע אֵינוֹ קוֹנֶה אוֹתוֹ מִיִּשְׂרָאֵל אֶלָּא בִּשְׁטָר וְאֵינוֹ מַקְנֶה אוֹתוֹ לְיִשְׂרָאֵל אֶלָּא בִּשְׁטָר שֶׁאֵין דַּעְתּוֹ סוֹמֶכֶת אֶלָּא עַל הַשְּׁטָר. לְפִיכָךְ יִשְׂרָאֵל שֶׁלָּקַח שָׂדֶה מִן הָעַכּוּ''ם וְנָתַן הַדָּמִים. וְקֹדֶם שֶׁיַּחְזִיק בָּהּ בָּא יִשְׂרָאֵל אַחֵר וְהֶחֱזִיק בָּהּ כְּדֶרֶךְ שֶׁמַּחֲזִיקִין בְּנִכְסֵי הַגֵּר זָכָה אַחֲרוֹן וְנוֹתֵן לָרִאשׁוֹן אֶת הַדָּמִים. מִפְּנֵי שֶׁהָעַכּוּ''ם מֵעֵת שֶׁלָּקַח הַדָּמִים סִלֵּק רְשׁוּתוֹ וְיִשְׂרָאֵל לֹא קָנָה עַד שֶׁיַּגִּיעַ הַשְּׁטָר לְיָדוֹ. וְנִמְצְאוּ נְכָסִים אֵלּוּ כְּנִכְסֵי מִדְבָּר שֶׁכָּל הַמַּחֲזִיק בָּהֶן זָכָה:
כסף משנה
14.
When a gentile sells movable property to a Jew or buys movable property, he acquires and transfers the property through meshichah or through the transfer of funds.
Different rules apply with regard to landed property. A gentile does not acquire landed property from a Jew without a deed of sale, nor does he transfer property without a deed of sale. For he will not rely on anything but a deed of sale.
For this reason, if a Jew purchased a field from a gentile and paid the money for it, but before he could manifest his ownership over it, another Jew came and manifested ownership over it in a manner similar to that described above with regard to the acquisition of the property of a deceased convert, the latter person acquires the land. He must, however, repay the money to the purchaser.
The rationale for the decision is that the gentile abrogates his ownership over the property at the time he receives the money. And yet, the Jew purchasing the land does not acquire it until the deed of sale reaches his hand. In the interim, the property is like property in the desert concerning which the rule is: Whoever manifests ownership over it acquires it.

הלכה טו
בַּמֶּה דְּבָרִים אֲמוּרִים בְּמָקוֹם שֶׁאֵין מִשְׁפָּט יָדוּעַ לַמֶּלֶךְ. אֲבָל אִם דִּין אוֹתוֹ הַמֶּלֶךְ וּמִשְׁפָּטוֹ שֶׁלֹּא יִזְכֶּה בַּקַּרְקַע אֶלָּא מִי שֶׁכּוֹתֵב בִּשְׁטָר אוֹ הַנּוֹתֵן דָּמִים וְכַיּוֹצֵא בִּדְבָרִים אֵלּוּ. עוֹשִׂין כְּפִי מִשְׁפַּט הַמֶּלֶךְ. שֶׁכָּל דִּינֵי הַמֶּלֶךְ בְּמָמוֹן עַל פִּיהֶן דָּנִין:
כסף משנה
15.
When does the above apply? When there are no known laws enforced by the governing sovereign. If, however, the law of the governing sovereign and his judgment is that only a person whose name is mentioned in the deed of sale - who paid money for the property or the like - can acquire the land, we follow the law of the governing sovereign. For we rule according to all the financial laws of the governing sovereign.

קניין הלכות זכייה ומתנה פרק א
Kinyan Zechiyah and Matanah Chapter 1